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| Meta Title | Differential Equations - Inverse Laplace Transforms |
| Meta Description | In this section we ask the opposite question from the previous section. In other words, given a Laplace transform, what function did we originally have? We again work a variety of examples illustrating how to use the table of Laplace transforms to do this as well as some of the manipulation of the given Laplace transform that is needed in order to use the table. |
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Section 4.3 : Inverse Laplace Transforms
Finding the Laplace transform of a function is not terribly difficult if we’ve got a table of transforms in front of us to use as we saw in the last
section
. What we would like to do now is go the other way.
We are going to be given a transform,
F
(
s
)
, and ask what function (or functions) did we have originally. As you will see this can be a more complicated and lengthy process than taking transforms. In these cases we say that we are finding the
Inverse Laplace Transform
of
F
(
s
)
and use the following notation.
f
(
t
)
=
L
−
1
{
F
(
s
)
}
As with Laplace transforms, we’ve got the following fact to help us take the inverse transform.
Fact
Given the two Laplace
transforms
F
(
s
)
and
G
(
s
)
then
L
−
1
{
a
F
(
s
)
+
b
G
(
s
)
}
=
a
L
−
1
{
F
(
s
)
}
+
b
L
−
1
{
G
(
s
)
}
for any constants
a
and
b
.
So, we take the inverse transform of the individual transforms, put any constants back in and then add or subtract the results back up.
Let’s take a look at a couple of fairly simple inverse transforms.
Example 1
Find the inverse transform of each of the following.
F
(
s
)
=
6
s
−
1
s
−
8
+
4
s
−
3
H
(
s
)
=
19
s
+
2
−
1
3
s
−
5
+
7
s
5
F
(
s
)
=
6
s
s
2
+
25
+
3
s
2
+
25
G
(
s
)
=
8
3
s
2
+
12
+
3
s
2
−
49
Show All Solutions
Hide All Solutions
Show Discussion
We’ve always felt that the key to doing inverse transforms is to look at the denominator and try to identify what you’ve got based on that. If there is only one entry in the table that has that particular denominator, the next step is to make sure the numerator is correctly set up for the inverse transform process. If it isn’t, correct it (this is always easy to do) and then take the inverse transform.
If there is more than one entry in the table that has a particular denominator, then the numerators of each will be different, so go up to the numerator and see which one you’ve got. If you need to correct the numerator to get it into the correct form and then take the inverse transform.
So, with this advice in mind let’s see if we can take some inverse transforms.
a
F
(
s
)
=
6
s
−
1
s
−
8
+
4
s
−
3
Show Solution
From the denominator of the first term it looks like the first term is just a constant. The correct numerator for this term is a “1” so we’ll just factor the 6 out before taking the inverse transform. The second term appears to be an exponential with
a
=
8
and the numerator is exactly what it needs to be. The third term also appears to be an exponential, only this time
a
=
3
and we’ll need to factor the 4 out before taking the inverse transforms.
So, with a little more detail than we’ll usually put into these,
F
(
s
)
=
6
1
s
−
1
s
−
8
+
4
1
s
−
3
f
(
t
)
=
6
(
1
)
−
e
8
t
+
4
(
e
3
t
)
=
6
−
e
8
t
+
4
e
3
t
b
H
(
s
)
=
19
s
+
2
−
1
3
s
−
5
+
7
s
5
Show Solution
The first term in this case looks like an exponential with
a
=
−
2
and we’ll need to factor out the 19. Be careful with negative signs in these problems, it’s very easy to lose track of them.
The second term almost looks like an exponential, except that it’s got a
3
s
instead of just an
s
in the denominator. It is an exponential, but in this case, we’ll need to factor a 3 out of the denominator before taking the inverse transform.
The denominator of the third term appears to be
#3
in the table with
n
=
4
. The numerator however, is not correct for this. There is currently a 7 in the numerator and we need a
4
!
=
24
in the numerator. This is very easy to fix. Whenever a numerator is off by a multiplicative constant, as in this case, all we need to do is put the constant that we need in the numerator. We will just need to remember to take it back out by dividing by the same constant.
So, let’s first rewrite the transform.
H
(
s
)
=
19
s
−
(
−
2
)
−
1
3
(
s
−
5
3
)
+
7
4
!
4
!
s
4
+
1
=
19
1
s
−
(
−
2
)
−
1
3
1
s
−
5
3
+
7
4
!
4
!
s
4
+
1
So, what did we do here? We factored the 19 out of the first term. We factored the 3 out of the denominator of the second term since it can’t be there for the inverse transform and in the third term we factored everything out of the numerator except the 4! since that is the portion that we need in the numerator for the inverse transform process.
Let’s now take the inverse transform.
h
(
t
)
=
19
e
−
2
t
−
1
3
e
5
t
3
+
7
24
t
4
c
F
(
s
)
=
6
s
s
2
+
25
+
3
s
2
+
25
Show Solution
In this part we’ve got the same denominator in both terms and our table tells us that we’ve either got
#7
or
#8
. The numerators will tell us which we’ve actually got. The first one has an
s
in the numerator and so this means that the first term must be #8 and we’ll need to factor the 6 out of the numerator in this case. The second term has only a constant in the numerator and so this term must be #7, however, in order for this to be exactly #7 we’ll need to multiply/divide a 5 in the numerator to get it correct for the table.
The transform becomes,
F
(
s
)
=
6
s
s
2
+
(
5
)
2
+
3
5
5
s
2
+
(
5
)
2
=
6
s
s
2
+
(
5
)
2
+
3
5
5
s
2
+
(
5
)
2
Taking the inverse transform gives,
f
(
t
)
=
6
cos
(
5
t
)
+
3
5
sin
(
5
t
)
d
G
(
s
)
=
8
3
s
2
+
12
+
3
s
2
−
49
Show Solution
In this case the first term will be a sine once we factor a 3 out of the denominator, while the second term appears to be a hyperbolic sine (
#17
). Again, be careful with the difference between these two. Both of the terms will also need to have their numerators fixed up. Here is the transform once we’re done rewriting it.
G
(
s
)
=
1
3
8
s
2
+
4
+
3
s
2
−
49
=
1
3
(
4
)
(
2
)
s
2
+
(
2
)
2
+
3
7
7
s
2
−
(
7
)
2
Notice that in the first term we took advantage of the fact that we could get the 2 in the numerator that we needed by factoring the 8. The inverse transform is then,
g
(
t
)
=
4
3
sin
(
2
t
)
+
3
7
sinh
(
7
t
)
So, probably the best way to identify the transform is by looking at the denominator. If there is more than one possibility use the numerator to identify the correct one. Fix up the numerator if needed to get it into the form needed for the inverse transform process. Finally, take the inverse transform.
Let’s do some slightly harder problems. These are a little more involved than the first set.
Example 2
Find the inverse transform of each of the following.
F
(
s
)
=
6
s
−
5
s
2
+
7
F
(
s
)
=
1
−
3
s
s
2
+
8
s
+
21
G
(
s
)
=
3
s
−
2
2
s
2
−
6
s
−
2
H
(
s
)
=
s
+
7
s
2
−
3
s
−
10
Show All Solutions
Hide All Solutions
a
F
(
s
)
=
6
s
−
5
s
2
+
7
Show Solution
From the denominator of this one it appears that it is either a sine or a cosine. However, the numerator doesn’t match up to either of these in the table. A cosine wants just an
s
in the numerator with at most a multiplicative constant, while a sine wants only a constant and no
s
in the numerator.
We’ve got both in the numerator. This is easy to fix however. We will just split up the transform into two terms and then do inverse transforms.
F
(
s
)
=
6
s
s
2
+
7
−
5
7
7
s
2
+
7
f
(
t
)
=
6
cos
(
7
t
)
−
5
7
sin
(
7
t
)
Do not get too used to always getting the perfect squares in sines and cosines that we saw in the first set of examples. More often than not (at least in my class) they won’t be perfect squares!
b
F
(
s
)
=
1
−
3
s
s
2
+
8
s
+
21
Show Solution
In this case there are no denominators in our table that look like this. We can however make the denominator look like one of the denominators in the table by completing the square on the denominator. So, let’s do that first.
s
2
+
8
s
+
21
=
s
2
+
8
s
+
16
−
16
+
21
=
s
2
+
8
s
+
16
+
5
=
(
s
+
4
)
2
+
5
Recall that in completing the square you take half the coefficient of the
s
, square this, and then add and subtract the result to the polynomial. After doing this the first three terms should factor as a perfect square.
So, the transform can be written as the following.
F
(
s
)
=
1
−
3
s
(
s
+
4
)
2
+
5
Okay, with this rewrite it looks like we’ve got
#19
and/or
#20
’s from our table of transforms. However, note that in order for it to be a
#19
we want just a constant in the numerator and in order to be a
#20
we need an
s
–
a
in the numerator. We’ve got neither of these, so we’ll have to correct the numerator to get it into proper form.
In correcting the numerator always get the
s
–
a
first. This is the important part. We will also need to be careful of the 3 that sits in front of the
s
. One way to take care of this is to break the term into two pieces, factor the 3 out of the second and then fix up the numerator of this term. This will work; however, it will put three terms into our answer and there are really only two terms.
So, we will leave the transform as a single term and correct it as follows,
F
(
s
)
=
1
−
3
(
s
+
4
−
4
)
(
s
+
4
)
2
+
5
=
1
−
3
(
s
+
4
)
+
12
(
s
+
4
)
2
+
5
=
−
3
(
s
+
4
)
+
13
(
s
+
4
)
2
+
5
We needed an
s
+
4
in the numerator, so we put that in. We just needed to make sure and take the 4 back out by subtracting it back out. Also, because of the 3 multiplying the
s
we needed to do all this inside a set of parenthesis. Then we partially multiplied the 3 through the second term and combined the constants. With the transform in this form, we can break it up into two transforms each of which are in the tables and so we can do inverse transforms on them,
F
(
s
)
=
−
3
s
+
4
(
s
+
4
)
2
+
5
+
13
5
5
(
s
+
4
)
2
+
5
f
(
t
)
=
−
3
e
−
4
t
cos
(
5
t
)
+
13
5
e
−
4
t
sin
(
5
t
)
c
G
(
s
)
=
3
s
−
2
2
s
2
−
6
s
−
2
Show Solution
This one is similar to the last one. We just need to be careful with the completing the square however. The first thing that we should do is factor a 2 out of the denominator, then complete the square. Remember that when completing the square a coefficient of 1 on the
s
2
term is needed! So, here’s the work for this transform.
G
(
s
)
=
3
s
−
2
2
(
s
2
−
3
s
−
1
)
=
1
2
3
s
−
2
s
2
−
3
s
+
9
4
−
9
4
−
1
=
1
2
3
s
−
2
(
s
−
3
2
)
2
−
13
4
So, it looks like we’ve got
#21
and
#22
with a corrected numerator. Here’s the work for that and the inverse transform.
G
(
s
)
=
1
2
3
(
s
−
3
2
+
3
2
)
−
2
(
s
−
3
2
)
2
−
13
4
=
1
2
3
(
s
−
3
2
)
+
5
2
(
s
−
3
2
)
2
−
13
4
=
1
2
(
3
(
s
−
3
2
)
(
s
−
3
2
)
2
−
13
4
+
5
2
13
13
(
s
−
3
2
)
2
−
13
4
)
g
(
t
)
=
1
2
(
3
e
3
t
2
cosh
(
13
2
t
)
+
5
13
e
3
t
2
sinh
(
13
2
t
)
)
In correcting the numerator of the second term, notice that I only put in the square root since we already had the “over 2” part of the fraction that we needed in the numerator.
d
H
(
s
)
=
s
+
7
s
2
−
3
s
−
10
Show Solution
This one appears to be similar to the previous two, but it actually isn’t. The denominators in the previous two couldn’t be easily factored. In this case the denominator does factor and so we need to deal with it differently. Here is the transform with the factored denominator.
H
(
s
)
=
s
+
7
(
s
+
2
)
(
s
−
5
)
The denominator of this transform seems to suggest that we’ve got a couple of exponentials, however in order to be exponentials there can only be a single term in the denominator and no
s
’s in the numerator.
To fix this we will need to do partial fractions on this transform. In this case the partial fraction decomposition will be
H
(
s
)
=
A
s
+
2
+
B
s
−
5
Don’t remember how to do partial fractions? In this example we’ll show you one way of getting the values of the constants and after this example we’ll review how to get the correct form of the partial fraction decomposition.
Okay, so let’s get the constants. There is a method for finding the constants that will always work, however it can lead to more work than is sometimes required. Eventually, we will need that method, however in this case there is an easier way to find the constants.
Regardless of the method used, the first step is to actually add the two terms back up. This gives the following.
s
+
7
(
s
+
2
)
(
s
−
5
)
=
A
(
s
−
5
)
+
B
(
s
+
2
)
(
s
+
2
)
(
s
−
5
)
Now, this needs to be true for any
s
that we should choose to put in. So, since the denominators are the same we just need to get the numerators equal. Therefore, set the numerators equal.
s
+
7
=
A
(
s
−
5
)
+
B
(
s
+
2
)
Again, this must be true for ANY value of
s
that we want to put in. So, let’s take advantage of that. If it must be true for any value of
s
then it must be true for
s
=
−
2
, to pick a value at random. In this case we get,
5
=
A
(
−
7
)
+
B
(
0
)
⇒
A
=
−
5
7
We found
A
by appropriately picking
s
. We can
B
in the same way if we chose
s
=
5
.
12
=
A
(
0
)
+
B
(
7
)
⇒
B
=
12
7
This will not always work, but when it does it will usually simplify the work considerably.
So, with these constants the transform becomes,
H
(
s
)
=
−
5
7
s
+
2
+
12
7
s
−
5
We can now easily do the inverse transform to get,
h
(
t
)
=
−
5
7
e
−
2
t
+
12
7
e
5
t
The last part of this example needed partial fractions to get the inverse transform. When we finally get back to differential equations and we start using Laplace
transforms to solve them, you will quickly come to understand that partial fractions are a fact of life in these problems. Almost every problem will require partial fractions to one degree or another.
Note that we could have done the last part of this example as we had done the previous two parts. If we had we would have gotten hyperbolic functions. However, recalling the
definition
of the hyperbolic functions we could have written the result in the form we got from the way we worked our problem. However, most students have a better feel for exponentials than they do for hyperbolic functions and so it’s usually best to just use partial fractions and get the answer in terms of exponentials. It may be a little more work, but it will give a nicer (and easier to work with) form of the answer.
Be warned that in my class I’ve got a rule that if the denominator can be factored with integer coefficients then it must be.
So, let’s remind you how to get the correct partial fraction decomposition. The first step is to factor the denominator as much as possible. Then for each term in the denominator we will use the following table to get a term or terms for our partial fraction decomposition.
Factor in
denominator
Term in partial
fraction decomposition
a
x
+
b
A
a
x
+
b
(
a
x
+
b
)
k
A
1
a
x
+
b
+
A
2
(
a
x
+
b
)
2
+
⋯
+
A
k
(
a
x
+
b
)
k
a
x
2
+
b
x
+
c
A
x
+
B
a
x
2
+
b
x
+
c
(
a
x
2
+
b
x
+
c
)
k
A
1
x
+
B
1
a
x
2
+
b
x
+
c
+
A
2
x
+
B
2
(
a
x
2
+
b
x
+
c
)
2
+
⋯
+
A
k
x
+
B
k
(
a
x
2
+
b
x
+
c
)
k
Notice that the first and third cases are really special cases of the second and fourth cases respectively.
So, let’s do a couple more examples to remind you how to do partial fractions.
Example 3
Find the inverse transform of each of the following.
G
(
s
)
=
86
s
−
78
(
s
+
3
)
(
s
−
4
)
(
5
s
−
1
)
F
(
s
)
=
2
−
5
s
(
s
−
6
)
(
s
2
+
11
)
G
(
s
)
=
25
s
3
(
s
2
+
4
s
+
5
)
Show All Solutions
Hide All Solutions
a
G
(
s
)
=
86
s
−
78
(
s
+
3
)
(
s
−
4
)
(
5
s
−
1
)
Show Solution
Here’s the partial fraction decomposition for this part.
G
(
s
)
=
A
s
+
3
+
B
s
−
4
+
C
5
s
−
1
Now, this time we won’t go into quite the detail as we did in the last example. We are after the numerator of the partial fraction decomposition and this is usually easy enough to do in our heads. Therefore, we will go straight to setting numerators equal.
86
s
−
78
=
A
(
s
−
4
)
(
5
s
−
1
)
+
B
(
s
+
3
)
(
5
s
−
1
)
+
C
(
s
+
3
)
(
s
−
4
)
As with the last example, we can easily get the constants by correctly picking values of
s
.
s
=
−
3
−
336
=
A
(
−
7
)
(
−
16
)
⇒
A
=
−
3
s
=
1
5
−
304
5
=
C
(
16
5
)
(
−
19
5
)
⇒
C
=
5
s
=
4
266
=
B
(
7
)
(
19
)
⇒
B
=
2
So, the partial fraction decomposition for this transform is,
G
(
s
)
=
−
3
s
+
3
+
2
s
−
4
+
5
5
s
−
1
Now, in order to actually take the inverse transform we will need to factor a 5 out of the denominator of the last term. The corrected transform as well as its inverse transform is.
G
(
s
)
=
−
3
s
+
3
+
2
s
−
4
+
1
s
−
1
5
g
(
t
)
=
−
3
e
−
3
t
+
2
e
4
t
+
e
t
5
b
F
(
s
)
=
2
−
5
s
(
s
−
6
)
(
s
2
+
11
)
Show Solution
So, for the first time we’ve got a quadratic in the denominator. Here’s the decomposition for this part.
F
(
s
)
=
A
s
−
6
+
B
s
+
C
s
2
+
11
Setting numerators equal gives,
2
−
5
s
=
A
(
s
2
+
11
)
+
(
B
s
+
C
)
(
s
−
6
)
Okay, in this case we could use
s
=
6
to quickly find
A
, but that’s all it would give. In this case we will need to go the “long” way around to getting the constants. Note that this way will always work but is sometimes more work than is required.
The “long” way is to completely multiply out the right side and collect like terms.
2
−
5
s
=
A
(
s
2
+
11
)
+
(
B
s
+
C
)
(
s
−
6
)
=
A
s
2
+
11
A
+
B
s
2
−
6
B
s
+
C
s
−
6
C
=
(
A
+
B
)
s
2
+
(
−
6
B
+
C
)
s
+
11
A
−
6
C
In order for these two to be equal the coefficients of the
s
2
,
s
and the constants must all be equal. So, setting coefficients equal gives the following system of equations that can be solved.
s
2
:
A
+
B
=
0
s
1
:
−
6
B
+
C
=
−
5
s
0
:
11
A
−
6
C
=
2
}
⇒
A
=
−
28
47
,
B
=
28
47
,
C
=
−
67
47
Notice that we used
s
0
to denote the constants. This is habit on my part and isn’t really required, it’s just what I’m used to doing. Also, the coefficients are fairly messy fractions in this case. Get used to that. They will often be like this when we get back into solving differential equations.
There is a way to make our life a little easier as well with this. Since all of the fractions have a denominator of 47 we’ll factor that out as we plug them back into the decomposition. This will make dealing with them much easier. The partial fraction decomposition is then,
F
(
s
)
=
1
47
(
−
28
s
−
6
+
28
s
−
67
s
2
+
11
)
=
1
47
(
−
28
s
−
6
+
28
s
s
2
+
11
−
67
11
11
s
2
+
11
)
The inverse transform is then.
f
(
t
)
=
1
47
(
−
28
e
6
t
+
28
cos
(
11
t
)
−
67
11
sin
(
11
t
)
)
c
G
(
s
)
=
25
s
3
(
s
2
+
4
s
+
5
)
Show Solution
With this last part do not get excited about the
s
3
. We can think of this term as
s
3
=
(
s
−
0
)
3
and it becomes a linear term to a power. So, the partial fraction decomposition is
G
(
s
)
=
A
s
+
B
s
2
+
C
s
3
+
D
s
+
E
s
2
+
4
s
+
5
Setting numerators equal and multiplying out gives.
25
=
A
s
2
(
s
2
+
4
s
+
5
)
+
B
s
(
s
2
+
4
s
+
5
)
+
C
(
s
2
+
4
s
+
5
)
+
(
D
s
+
E
)
s
3
=
(
A
+
D
)
s
4
+
(
4
A
+
B
+
E
)
s
3
+
(
5
A
+
4
B
+
C
)
s
2
+
(
5
B
+
4
C
)
s
+
5
C
Setting coefficients equal gives the following system.
s
4
:
A
+
D
=
0
s
3
:
4
A
+
B
+
E
=
0
s
2
:
5
A
+
4
B
+
C
=
0
s
1
:
5
B
+
4
C
=
0
s
0
:
5
C
=
25
}
⇒
A
=
11
5
,
B
=
−
4
,
C
=
5
,
D
=
−
11
5
,
E
=
−
24
5
This system looks messy, but it’s easier to solve than it might look. First, we get
C
for free from the last equation. We can then use the fourth equation to find
B
. The third equation will then give
A
,
etc
.
When plugging into the decomposition we’ll get everything with a denominator of 5, then factor that out as we did in the previous part in order to make things easier to deal with.
G
(
s
)
=
1
5
(
11
s
−
20
s
2
+
25
s
3
−
11
s
+
24
s
2
+
4
s
+
5
)
Note that we also factored a minus sign out of the last two terms. To complete this part we’ll need to complete the square on the later term and fix up a couple of numerators. Here’s that work.
G
(
s
)
=
1
5
(
11
s
−
20
s
2
+
25
s
3
−
11
s
+
24
s
2
+
4
s
+
5
)
=
1
5
(
11
s
−
20
s
2
+
25
s
3
−
11
(
s
+
2
−
2
)
+
24
(
s
+
2
)
2
+
1
)
=
1
5
(
11
s
−
20
s
2
+
25
2
!
2
!
s
3
−
11
(
s
+
2
)
(
s
+
2
)
2
+
1
−
2
(
s
+
2
)
2
+
1
)
The inverse transform is then.
g
(
t
)
=
1
5
(
11
−
20
t
+
25
2
t
2
−
11
e
−
2
t
cos
(
t
)
−
2
e
−
2
t
sin
(
t
)
)
So, one final time. Partial fractions are a fact of life when using Laplace
transforms to solve differential equations. Make sure that you can deal with them. |
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- [1\.6 Trig Equations with Calculators, Part II](https://tutorial.math.lamar.edu/Classes/CalcI/TrigEquations_CalcII.aspx)
- [1\.7 Exponential Functions](https://tutorial.math.lamar.edu/Classes/CalcI/ExpFunctions.aspx)
- [1\.8 Logarithm Functions](https://tutorial.math.lamar.edu/Classes/CalcI/LogFcns.aspx)
- [1\.9 Exponential and Logarithm Equations](https://tutorial.math.lamar.edu/Classes/CalcI/ExpLogEqns.aspx)
- [1\.10 Common Graphs](https://tutorial.math.lamar.edu/Classes/CalcI/CommonGraphs.aspx)
[Close submenu (2. Limits)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-10)[2\. Limits](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-10)[Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/[Calculus I](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-10)/2\. Limits
- [2\.1 Tangent Lines and Rates of Change](https://tutorial.math.lamar.edu/Classes/CalcI/Tangents_Rates.aspx)
- [2\.2 The Limit](https://tutorial.math.lamar.edu/Classes/CalcI/TheLimit.aspx)
- [2\.3 One-Sided Limits](https://tutorial.math.lamar.edu/Classes/CalcI/OneSidedLimits.aspx)
- [2\.4 Limit Properties](https://tutorial.math.lamar.edu/Classes/CalcI/LimitsProperties.aspx)
- [2\.5 Computing Limits](https://tutorial.math.lamar.edu/Classes/CalcI/ComputingLimits.aspx)
- [2\.6 Infinite Limits](https://tutorial.math.lamar.edu/Classes/CalcI/InfiniteLimits.aspx)
- [2\.7 Limits At Infinity, Part I](https://tutorial.math.lamar.edu/Classes/CalcI/LimitsAtInfinityI.aspx)
- [2\.8 Limits At Infinity, Part II](https://tutorial.math.lamar.edu/Classes/CalcI/LimitsAtInfinityII.aspx)
- [2\.9 Continuity](https://tutorial.math.lamar.edu/Classes/CalcI/Continuity.aspx)
- [2\.10 The Definition of the Limit](https://tutorial.math.lamar.edu/Classes/CalcI/DefnOfLimit.aspx)
[Close submenu (3. Derivatives)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-10)[3\. Derivatives](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-10)[Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/[Calculus I](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-10)/3\. Derivatives
- [3\.1 The Definition of the Derivative](https://tutorial.math.lamar.edu/Classes/CalcI/DefnOfDerivative.aspx)
- [3\.2 Interpretation of the Derivative](https://tutorial.math.lamar.edu/Classes/CalcI/DerivativeInterp.aspx)
- [3\.3 Differentiation Formulas](https://tutorial.math.lamar.edu/Classes/CalcI/DiffFormulas.aspx)
- [3\.4 Product and Quotient Rule](https://tutorial.math.lamar.edu/Classes/CalcI/ProductQuotientRule.aspx)
- [3\.5 Derivatives of Trig Functions](https://tutorial.math.lamar.edu/Classes/CalcI/DiffTrigFcns.aspx)
- [3\.6 Derivatives of Exponential and Logarithm Functions](https://tutorial.math.lamar.edu/Classes/CalcI/DiffExpLogFcns.aspx)
- [3\.7 Derivatives of Inverse Trig Functions](https://tutorial.math.lamar.edu/Classes/CalcI/DiffInvTrigFcns.aspx)
- [3\.8 Derivatives of Hyperbolic Functions](https://tutorial.math.lamar.edu/Classes/CalcI/DiffHyperFcns.aspx)
- [3\.9 Chain Rule](https://tutorial.math.lamar.edu/Classes/CalcI/ChainRule.aspx)
- [3\.10 Implicit Differentiation](https://tutorial.math.lamar.edu/Classes/CalcI/ImplicitDIff.aspx)
- [3\.11 Related Rates](https://tutorial.math.lamar.edu/Classes/CalcI/RelatedRates.aspx)
- [3\.12 Higher Order Derivatives](https://tutorial.math.lamar.edu/Classes/CalcI/HigherOrderDerivatives.aspx)
- [3\.13 Logarithmic Differentiation](https://tutorial.math.lamar.edu/Classes/CalcI/LogDiff.aspx)
[Close submenu (4. Applications of Derivatives)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-10)[4\. Applications of Derivatives](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-10)[Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/[Calculus I](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-10)/4\. Applications of Derivatives
- [4\.1 Rates of Change](https://tutorial.math.lamar.edu/Classes/CalcI/RateOfChange.aspx)
- [4\.2 Critical Points](https://tutorial.math.lamar.edu/Classes/CalcI/CriticalPoints.aspx)
- [4\.3 Minimum and Maximum Values](https://tutorial.math.lamar.edu/Classes/CalcI/MinMaxValues.aspx)
- [4\.4 Finding Absolute Extrema](https://tutorial.math.lamar.edu/Classes/CalcI/AbsExtrema.aspx)
- [4\.5 The Shape of a Graph, Part I](https://tutorial.math.lamar.edu/Classes/CalcI/ShapeofGraphPtI.aspx)
- [4\.6 The Shape of a Graph, Part II](https://tutorial.math.lamar.edu/Classes/CalcI/ShapeofGraphPtII.aspx)
- [4\.7 The Mean Value Theorem](https://tutorial.math.lamar.edu/Classes/CalcI/MeanValueTheorem.aspx)
- [4\.8 Optimization](https://tutorial.math.lamar.edu/Classes/CalcI/Optimization.aspx)
- [4\.9 More Optimization Problems](https://tutorial.math.lamar.edu/Classes/CalcI/MoreOptimization.aspx)
- [4\.10 L'Hospital's Rule and Indeterminate Forms](https://tutorial.math.lamar.edu/Classes/CalcI/LHospitalsRule.aspx)
- [4\.11 Linear Approximations](https://tutorial.math.lamar.edu/Classes/CalcI/LinearApproximations.aspx)
- [4\.12 Differentials](https://tutorial.math.lamar.edu/Classes/CalcI/Differentials.aspx)
- [4\.13 Newton's Method](https://tutorial.math.lamar.edu/Classes/CalcI/NewtonsMethod.aspx)
- [4\.14 Business Applications](https://tutorial.math.lamar.edu/Classes/CalcI/BusinessApps.aspx)
[Close submenu (5. Integrals)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-10)[5\. Integrals](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-10)[Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/[Calculus I](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-10)/5\. Integrals
- [5\.1 Indefinite Integrals](https://tutorial.math.lamar.edu/Classes/CalcI/IndefiniteIntegrals.aspx)
- [5\.2 Computing Indefinite Integrals](https://tutorial.math.lamar.edu/Classes/CalcI/ComputingIndefiniteIntegrals.aspx)
- [5\.3 Substitution Rule for Indefinite Integrals](https://tutorial.math.lamar.edu/Classes/CalcI/SubstitutionRuleIndefinite.aspx)
- [5\.4 More Substitution Rule](https://tutorial.math.lamar.edu/Classes/CalcI/SubstitutionRuleIndefinitePtII.aspx)
- [5\.5 Area Problem](https://tutorial.math.lamar.edu/Classes/CalcI/AreaProblem.aspx)
- [5\.6 Definition of the Definite Integral](https://tutorial.math.lamar.edu/Classes/CalcI/DefnOfDefiniteIntegral.aspx)
- [5\.7 Computing Definite Integrals](https://tutorial.math.lamar.edu/Classes/CalcI/ComputingDefiniteIntegrals.aspx)
- [5\.8 Substitution Rule for Definite Integrals](https://tutorial.math.lamar.edu/Classes/CalcI/SubstitutionRuleDefinite.aspx)
[Close submenu (6. Applications of Integrals)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-10)[6\. Applications of Integrals](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-10)[Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/[Calculus I](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-10)/6\. Applications of Integrals
- [6\.1 Average Function Value](https://tutorial.math.lamar.edu/Classes/CalcI/AvgFcnValue.aspx)
- [6\.2 Area Between Curves](https://tutorial.math.lamar.edu/Classes/CalcI/AreaBetweenCurves.aspx)
- [6\.3 Volumes of Solids of Revolution / Method of Rings](https://tutorial.math.lamar.edu/Classes/CalcI/VolumeWithRings.aspx)
- [6\.4 Volumes of Solids of Revolution/Method of Cylinders](https://tutorial.math.lamar.edu/Classes/CalcI/VolumeWithCylinder.aspx)
- [6\.5 More Volume Problems](https://tutorial.math.lamar.edu/Classes/CalcI/MoreVolume.aspx)
- [6\.6 Work](https://tutorial.math.lamar.edu/Classes/CalcI/Work.aspx)
[Close submenu (Appendix A. Extras)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-10)[Appendix A. Extras](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-10)[Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/[Calculus I](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-10)/Appendix A. Extras
- [A.1 Proof of Various Limit Properties](https://tutorial.math.lamar.edu/Classes/CalcI/LimitProofs.aspx)
- [A.2 Proof of Various Derivative Properties](https://tutorial.math.lamar.edu/Classes/CalcI/DerivativeProofs.aspx)
- [A.3 Proof of Trig Limits](https://tutorial.math.lamar.edu/Classes/CalcI/ProofTrigDeriv.aspx)
- [A.4 Proofs of Derivative Applications Facts](https://tutorial.math.lamar.edu/Classes/CalcI/DerivativeAppsProofs.aspx)
- [A.5 Proof of Various Integral Properties](https://tutorial.math.lamar.edu/Classes/CalcI/ProofIntProp.aspx)
- [A.6 Area and Volume Formulas](https://tutorial.math.lamar.edu/Classes/CalcI/Area_Volume_Formulas.aspx)
- [A.7 Types of Infinity](https://tutorial.math.lamar.edu/Classes/CalcI/TypesOfInfinity.aspx)
- [A.8 Summation Notation](https://tutorial.math.lamar.edu/Classes/CalcI/SummationNotation.aspx)
- [A.9 Constant of Integration](https://tutorial.math.lamar.edu/Classes/CalcI/ConstantofIntegration.aspx)
[Close submenu (Calculus II)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)[Calculus II](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)[Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/Calculus II
- [Open submenu (7. Integration Techniques)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-19)[7\. Integration Techniques](https://tutorial.math.lamar.edu/Classes/CalcII/IntTechIntro.aspx)
- [Open submenu (8. Applications of Integrals)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-20)[8\. Applications of Integrals](https://tutorial.math.lamar.edu/Classes/CalcII/IntAppsIntro.aspx)
- [Open submenu (9. Parametric Equations and Polar Coordinates)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-21)[9\. Parametric Equations and Polar Coordinates](https://tutorial.math.lamar.edu/Classes/CalcII/ParametricIntro.aspx)
- [Open submenu (10. Series & Sequences)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-22)[10\. Series & Sequences](https://tutorial.math.lamar.edu/Classes/CalcII/SeriesIntro.aspx)
- [Open submenu (11. Vectors)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-23)[11\. Vectors](https://tutorial.math.lamar.edu/Classes/CalcII/VectorsIntro.aspx)
- [Open submenu (12. 3-Dimensional Space)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-24)[12\. 3-Dimensional Space](https://tutorial.math.lamar.edu/Classes/CalcII/3DSpace.aspx)
[Close submenu (7. Integration Techniques)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-18)[7\. Integration Techniques](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-18)[Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/[Calculus II](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-18)/7\. Integration Techniques
- [7\.1 Integration by Parts](https://tutorial.math.lamar.edu/Classes/CalcII/IntegrationByParts.aspx)
- [7\.2 Integrals Involving Trig Functions](https://tutorial.math.lamar.edu/Classes/CalcII/IntegralsWithTrig.aspx)
- [7\.3 Trig Substitutions](https://tutorial.math.lamar.edu/Classes/CalcII/TrigSubstitutions.aspx)
- [7\.4 Partial Fractions](https://tutorial.math.lamar.edu/Classes/CalcII/PartialFractions.aspx)
- [7\.5 Integrals Involving Roots](https://tutorial.math.lamar.edu/Classes/CalcII/IntegralsWithRoots.aspx)
- [7\.6 Integrals Involving Quadratics](https://tutorial.math.lamar.edu/Classes/CalcII/IntegralsWithQuadratics.aspx)
- [7\.7 Integration Strategy](https://tutorial.math.lamar.edu/Classes/CalcII/IntegrationStrategy.aspx)
- [7\.8 Improper Integrals](https://tutorial.math.lamar.edu/Classes/CalcII/ImproperIntegrals.aspx)
- [7\.9 Comparison Test for Improper Integrals](https://tutorial.math.lamar.edu/Classes/CalcII/ImproperIntegralsCompTest.aspx)
- [7\.10 Approximating Definite Integrals](https://tutorial.math.lamar.edu/Classes/CalcII/ApproximatingDefIntegrals.aspx)
[Close submenu (8. Applications of Integrals)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-18)[8\. Applications of Integrals](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-18)[Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/[Calculus II](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-18)/8\. Applications of Integrals
- [8\.1 Arc Length](https://tutorial.math.lamar.edu/Classes/CalcII/ArcLength.aspx)
- [8\.2 Surface Area](https://tutorial.math.lamar.edu/Classes/CalcII/SurfaceArea.aspx)
- [8\.3 Center of Mass](https://tutorial.math.lamar.edu/Classes/CalcII/CenterOfMass.aspx)
- [8\.4 Hydrostatic Pressure](https://tutorial.math.lamar.edu/Classes/CalcII/HydrostaticPressure.aspx)
- [8\.5 Probability](https://tutorial.math.lamar.edu/Classes/CalcII/Probability.aspx)
[Close submenu (9. Parametric Equations and Polar Coordinates)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-18)[9\. Parametric Equations and Polar Coordinates](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-18)[Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/[Calculus II](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-18)/9\. Parametric Equations and Polar Coordinates
- [9\.1 Parametric Equations and Curves](https://tutorial.math.lamar.edu/Classes/CalcII/ParametricEqn.aspx)
- [9\.2 Tangents with Parametric Equations](https://tutorial.math.lamar.edu/Classes/CalcII/ParaTangent.aspx)
- [9\.3 Area with Parametric Equations](https://tutorial.math.lamar.edu/Classes/CalcII/ParaArea.aspx)
- [9\.4 Arc Length with Parametric Equations](https://tutorial.math.lamar.edu/Classes/CalcII/ParaArcLength.aspx)
- [9\.5 Surface Area with Parametric Equations](https://tutorial.math.lamar.edu/Classes/CalcII/ParaSurfaceArea.aspx)
- [9\.6 Polar Coordinates](https://tutorial.math.lamar.edu/Classes/CalcII/PolarCoordinates.aspx)
- [9\.7 Tangents with Polar Coordinates](https://tutorial.math.lamar.edu/Classes/CalcII/PolarTangents.aspx)
- [9\.8 Area with Polar Coordinates](https://tutorial.math.lamar.edu/Classes/CalcII/PolarArea.aspx)
- [9\.9 Arc Length with Polar Coordinates](https://tutorial.math.lamar.edu/Classes/CalcII/PolarArcLength.aspx)
- [9\.10 Surface Area with Polar Coordinates](https://tutorial.math.lamar.edu/Classes/CalcII/PolarSurfaceArea.aspx)
- [9\.11 Arc Length and Surface Area Revisited](https://tutorial.math.lamar.edu/Classes/CalcII/ArcLength_SurfaceArea.aspx)
[Close submenu (10. Series & Sequences)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-18)[10\. Series & Sequences](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-18)[Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/[Calculus II](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-18)/10\. Series & Sequences
- [10\.1 Sequences](https://tutorial.math.lamar.edu/Classes/CalcII/Sequences.aspx)
- [10\.2 More on Sequences](https://tutorial.math.lamar.edu/Classes/CalcII/MoreSequences.aspx)
- [10\.3 Series - The Basics](https://tutorial.math.lamar.edu/Classes/CalcII/Series_Basics.aspx)
- [10\.4 Convergence/Divergence of Series](https://tutorial.math.lamar.edu/Classes/CalcII/ConvergenceOfSeries.aspx)
- [10\.5 Special Series](https://tutorial.math.lamar.edu/Classes/CalcII/Series_Special.aspx)
- [10\.6 Integral Test](https://tutorial.math.lamar.edu/Classes/CalcII/IntegralTest.aspx)
- [10\.7 Comparison Test/Limit Comparison Test](https://tutorial.math.lamar.edu/Classes/CalcII/SeriesCompTest.aspx)
- [10\.8 Alternating Series Test](https://tutorial.math.lamar.edu/Classes/CalcII/AlternatingSeries.aspx)
- [10\.9 Absolute Convergence](https://tutorial.math.lamar.edu/Classes/CalcII/AbsoluteConvergence.aspx)
- [10\.10 Ratio Test](https://tutorial.math.lamar.edu/Classes/CalcII/RatioTest.aspx)
- [10\.11 Root Test](https://tutorial.math.lamar.edu/Classes/CalcII/RootTest.aspx)
- [10\.12 Strategy for Series](https://tutorial.math.lamar.edu/Classes/CalcII/SeriesStrategy.aspx)
- [10\.13 Estimating the Value of a Series](https://tutorial.math.lamar.edu/Classes/CalcII/EstimatingSeries.aspx)
- [10\.14 Power Series](https://tutorial.math.lamar.edu/Classes/CalcII/PowerSeries.aspx)
- [10\.15 Power Series and Functions](https://tutorial.math.lamar.edu/Classes/CalcII/PowerSeriesandFunctions.aspx)
- [10\.16 Taylor Series](https://tutorial.math.lamar.edu/Classes/CalcII/TaylorSeries.aspx)
- [10\.17 Applications of Series](https://tutorial.math.lamar.edu/Classes/CalcII/TaylorSeriesApps.aspx)
- [10\.18 Binomial Series](https://tutorial.math.lamar.edu/Classes/CalcII/BinomialSeries.aspx)
[Close submenu (11. Vectors)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-18)[11\. Vectors](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-18)[Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/[Calculus II](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-18)/11\. Vectors
- [11\.1 Vectors - The Basics](https://tutorial.math.lamar.edu/Classes/CalcII/Vectors_Basics.aspx)
- [11\.2 Vector Arithmetic](https://tutorial.math.lamar.edu/Classes/CalcII/VectorArithmetic.aspx)
- [11\.3 Dot Product](https://tutorial.math.lamar.edu/Classes/CalcII/DotProduct.aspx)
- [11\.4 Cross Product](https://tutorial.math.lamar.edu/Classes/CalcII/CrossProduct.aspx)
[Close submenu (12. 3-Dimensional Space)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-18)[12\. 3-Dimensional Space](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-18)[Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/[Calculus II](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-18)/12\. 3-Dimensional Space
- [12\.1 The 3-D Coordinate System](https://tutorial.math.lamar.edu/Classes/CalcII/3DCoords.aspx)
- [12\.2 Equations of Lines](https://tutorial.math.lamar.edu/Classes/CalcII/EqnsOfLines.aspx)
- [12\.3 Equations of Planes](https://tutorial.math.lamar.edu/Classes/CalcII/EqnsOfPlanes.aspx)
- [12\.4 Quadric Surfaces](https://tutorial.math.lamar.edu/Classes/CalcII/QuadricSurfaces.aspx)
- [12\.5 Functions of Several Variables](https://tutorial.math.lamar.edu/Classes/CalcII/MultiVrbleFcns.aspx)
- [12\.6 Vector Functions](https://tutorial.math.lamar.edu/Classes/CalcII/VectorFunctions.aspx)
- [12\.7 Calculus with Vector Functions](https://tutorial.math.lamar.edu/Classes/CalcII/VectorFcnsCalculus.aspx)
- [12\.8 Tangent, Normal and Binormal Vectors](https://tutorial.math.lamar.edu/Classes/CalcII/TangentNormalVectors.aspx)
- [12\.9 Arc Length with Vector Functions](https://tutorial.math.lamar.edu/Classes/CalcII/VectorArcLength.aspx)
- [12\.10 Curvature](https://tutorial.math.lamar.edu/Classes/CalcII/Curvature.aspx)
- [12\.11 Velocity and Acceleration](https://tutorial.math.lamar.edu/Classes/CalcII/Velocity_Acceleration.aspx)
- [12\.12 Cylindrical Coordinates](https://tutorial.math.lamar.edu/Classes/CalcII/CylindricalCoords.aspx)
- [12\.13 Spherical Coordinates](https://tutorial.math.lamar.edu/Classes/CalcII/SphericalCoords.aspx)
[Close submenu (Calculus III)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)[Calculus III](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)[Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/Calculus III
- [Open submenu (12. 3-Dimensional Space)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-26)[12\. 3-Dimensional Space](https://tutorial.math.lamar.edu/Classes/CalcIII/3DSpace.aspx)
- [Open submenu (13. Partial Derivatives)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-27)[13\. Partial Derivatives](https://tutorial.math.lamar.edu/Classes/CalcIII/PartialDerivsIntro.aspx)
- [Open submenu (14. Applications of Partial Derivatives)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-28)[14\. Applications of Partial Derivatives](https://tutorial.math.lamar.edu/Classes/CalcIII/PartialDerivAppsIntro.aspx)
- [Open submenu (15. Multiple Integrals)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-29)[15\. Multiple Integrals](https://tutorial.math.lamar.edu/Classes/CalcIII/MultipleIntegralsIntro.aspx)
- [Open submenu (16. Line Integrals)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-30)[16\. Line Integrals](https://tutorial.math.lamar.edu/Classes/CalcIII/LineIntegralsIntro.aspx)
- [Open submenu (17.Surface Integrals)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-31)[17\.Surface Integrals](https://tutorial.math.lamar.edu/Classes/CalcIII/SurfaceIntegralsIntro.aspx)
[Close submenu (12. 3-Dimensional Space)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-25)[12\. 3-Dimensional Space](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-25)[Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/[Calculus III](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-25)/12\. 3-Dimensional Space
- [12\.1 The 3-D Coordinate System](https://tutorial.math.lamar.edu/Classes/CalcIII/3DCoords.aspx)
- [12\.2 Equations of Lines](https://tutorial.math.lamar.edu/Classes/CalcIII/EqnsOfLines.aspx)
- [12\.3 Equations of Planes](https://tutorial.math.lamar.edu/Classes/CalcIII/EqnsOfPlanes.aspx)
- [12\.4 Quadric Surfaces](https://tutorial.math.lamar.edu/Classes/CalcIII/QuadricSurfaces.aspx)
- [12\.5 Functions of Several Variables](https://tutorial.math.lamar.edu/Classes/CalcIII/MultiVrbleFcns.aspx)
- [12\.6 Vector Functions](https://tutorial.math.lamar.edu/Classes/CalcIII/VectorFunctions.aspx)
- [12\.7 Calculus with Vector Functions](https://tutorial.math.lamar.edu/Classes/CalcIII/VectorFcnsCalculus.aspx)
- [12\.8 Tangent, Normal and Binormal Vectors](https://tutorial.math.lamar.edu/Classes/CalcIII/TangentNormalVectors.aspx)
- [12\.9 Arc Length with Vector Functions](https://tutorial.math.lamar.edu/Classes/CalcIII/VectorArcLength.aspx)
- [12\.10 Curvature](https://tutorial.math.lamar.edu/Classes/CalcIII/Curvature.aspx)
- [12\.11 Velocity and Acceleration](https://tutorial.math.lamar.edu/Classes/CalcIII/Velocity_Acceleration.aspx)
- [12\.12 Cylindrical Coordinates](https://tutorial.math.lamar.edu/Classes/CalcIII/CylindricalCoords.aspx)
- [12\.13 Spherical Coordinates](https://tutorial.math.lamar.edu/Classes/CalcIII/SphericalCoords.aspx)
[Close submenu (13. Partial Derivatives)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-25)[13\. Partial Derivatives](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-25)[Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/[Calculus III](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-25)/13\. Partial Derivatives
- [13\.1 Limits](https://tutorial.math.lamar.edu/Classes/CalcIII/Limits.aspx)
- [13\.2 Partial Derivatives](https://tutorial.math.lamar.edu/Classes/CalcIII/PartialDerivatives.aspx)
- [13\.3 Interpretations of Partial Derivatives](https://tutorial.math.lamar.edu/Classes/CalcIII/PartialDerivInterp.aspx)
- [13\.4 Higher Order Partial Derivatives](https://tutorial.math.lamar.edu/Classes/CalcIII/HighOrderPartialDerivs.aspx)
- [13\.5 Differentials](https://tutorial.math.lamar.edu/Classes/CalcIII/Differentials.aspx)
- [13\.6 Chain Rule](https://tutorial.math.lamar.edu/Classes/CalcIII/ChainRule.aspx)
- [13\.7 Directional Derivatives](https://tutorial.math.lamar.edu/Classes/CalcIII/DirectionalDeriv.aspx)
[Close submenu (14. Applications of Partial Derivatives)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-25)[14\. Applications of Partial Derivatives](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-25)[Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/[Calculus III](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-25)/14\. Applications of Partial Derivatives
- [14\.1 Tangent Planes and Linear Approximations](https://tutorial.math.lamar.edu/Classes/CalcIII/TangentPlanes.aspx)
- [14\.2 Gradient Vector, Tangent Planes and Normal Lines](https://tutorial.math.lamar.edu/Classes/CalcIII/GradientVectorTangentPlane.aspx)
- [14\.3 Relative Minimums and Maximums](https://tutorial.math.lamar.edu/Classes/CalcIII/RelativeExtrema.aspx)
- [14\.4 Absolute Minimums and Maximums](https://tutorial.math.lamar.edu/Classes/CalcIII/AbsoluteExtrema.aspx)
- [14\.5 Lagrange Multipliers](https://tutorial.math.lamar.edu/Classes/CalcIII/LagrangeMultipliers.aspx)
[Close submenu (15. Multiple Integrals)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-25)[15\. Multiple Integrals](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-25)[Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/[Calculus III](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-25)/15\. Multiple Integrals
- [15\.1 Double Integrals](https://tutorial.math.lamar.edu/Classes/CalcIII/DoubleIntegrals.aspx)
- [15\.2 Iterated Integrals](https://tutorial.math.lamar.edu/Classes/CalcIII/IteratedIntegrals.aspx)
- [15\.3 Double Integrals over General Regions](https://tutorial.math.lamar.edu/Classes/CalcIII/DIGeneralRegion.aspx)
- [15\.4 Double Integrals in Polar Coordinates](https://tutorial.math.lamar.edu/Classes/CalcIII/DIPolarCoords.aspx)
- [15\.5 Triple Integrals](https://tutorial.math.lamar.edu/Classes/CalcIII/TripleIntegrals.aspx)
- [15\.6 Triple Integrals in Cylindrical Coordinates](https://tutorial.math.lamar.edu/Classes/CalcIII/TICylindricalCoords.aspx)
- [15\.7 Triple Integrals in Spherical Coordinates](https://tutorial.math.lamar.edu/Classes/CalcIII/TISphericalCoords.aspx)
- [15\.8 Change of Variables](https://tutorial.math.lamar.edu/Classes/CalcIII/ChangeOfVariables.aspx)
- [15\.9 Surface Area](https://tutorial.math.lamar.edu/Classes/CalcIII/SurfaceArea.aspx)
- [15\.10 Area and Volume Revisited](https://tutorial.math.lamar.edu/Classes/CalcIII/Area_Volume.aspx)
[Close submenu (16. Line Integrals)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-25)[16\. Line Integrals](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-25)[Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/[Calculus III](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-25)/16\. Line Integrals
- [16\.1 Vector Fields](https://tutorial.math.lamar.edu/Classes/CalcIII/VectorFields.aspx)
- [16\.2 Line Integrals - Part I](https://tutorial.math.lamar.edu/Classes/CalcIII/LineIntegralsPtI.aspx)
- [16\.3 Line Integrals - Part II](https://tutorial.math.lamar.edu/Classes/CalcIII/LineIntegralsPtII.aspx)
- [16\.4 Line Integrals of Vector Fields](https://tutorial.math.lamar.edu/Classes/CalcIII/LineIntegralsVectorFields.aspx)
- [16\.5 Fundamental Theorem for Line Integrals](https://tutorial.math.lamar.edu/Classes/CalcIII/FundThmLineIntegrals.aspx)
- [16\.6 Conservative Vector Fields](https://tutorial.math.lamar.edu/Classes/CalcIII/ConservativeVectorField.aspx)
- [16\.7 Green's Theorem](https://tutorial.math.lamar.edu/Classes/CalcIII/GreensTheorem.aspx)
[Close submenu (17.Surface Integrals)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-25)[17\.Surface Integrals](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-25)[Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/[Calculus III](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-25)/17\.Surface Integrals
- [17\.1 Curl and Divergence](https://tutorial.math.lamar.edu/Classes/CalcIII/CurlDivergence.aspx)
- [17\.2 Parametric Surfaces](https://tutorial.math.lamar.edu/Classes/CalcIII/ParametricSurfaces.aspx)
- [17\.3 Surface Integrals](https://tutorial.math.lamar.edu/Classes/CalcIII/SurfaceIntegrals.aspx)
- [17\.4 Surface Integrals of Vector Fields](https://tutorial.math.lamar.edu/Classes/CalcIII/SurfIntVectorField.aspx)
- [17\.5 Stokes' Theorem](https://tutorial.math.lamar.edu/Classes/CalcIII/StokesTheorem.aspx)
- [17\.6 Divergence Theorem](https://tutorial.math.lamar.edu/Classes/CalcIII/DivergenceTheorem.aspx)
[Close submenu (Differential Equations)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)[Differential Equations](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)[Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/Differential Equations
- [Open submenu (1. Basic Concepts)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-33)[1\. Basic Concepts](https://tutorial.math.lamar.edu/Classes/DE/IntroBasic.aspx)
- [Open submenu (2. First Order DE's)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-34)[2\. First Order DE's](https://tutorial.math.lamar.edu/Classes/DE/IntroFirstOrder.aspx)
- [Open submenu (3. Second Order DE's)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-35)[3\. Second Order DE's](https://tutorial.math.lamar.edu/Classes/DE/IntroSecondOrder.aspx)
- [Open submenu (4. Laplace Transforms)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-36)[4\. Laplace Transforms](https://tutorial.math.lamar.edu/Classes/DE/LaplaceIntro.aspx)
- [Open submenu (5. Systems of DE's)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-37)[5\. Systems of DE's](https://tutorial.math.lamar.edu/Classes/DE/SystemsIntro.aspx)
- [Open submenu (6. Series Solutions to DE's)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-38)[6\. Series Solutions to DE's](https://tutorial.math.lamar.edu/Classes/DE/SeriesIntro.aspx)
- [Open submenu (7. Higher Order Differential Equations)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-39)[7\. Higher Order Differential Equations](https://tutorial.math.lamar.edu/Classes/DE/IntroHigherOrder.aspx)
- [Open submenu (8. Boundary Value Problems & Fourier Series)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-40)[8\. Boundary Value Problems & Fourier Series](https://tutorial.math.lamar.edu/Classes/DE/IntroBVP.aspx)
- [Open submenu (9. Partial Differential Equations )](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-41)[9\. Partial Differential Equations](https://tutorial.math.lamar.edu/Classes/DE/IntroPDE.aspx)
[Close submenu (1. Basic Concepts)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-32)[1\. Basic Concepts](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-32)[Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/[Differential Equations](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-32)/1\. Basic Concepts
- [1\.1 Definitions](https://tutorial.math.lamar.edu/Classes/DE/Definitions.aspx)
- [1\.2 Direction Fields](https://tutorial.math.lamar.edu/Classes/DE/DirectionFields.aspx)
- [1\.3 Final Thoughts](https://tutorial.math.lamar.edu/Classes/DE/FinalThoughts.aspx)
[Close submenu (2. First Order DE's)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-32)[2\. First Order DE's](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-32)[Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/[Differential Equations](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-32)/2\. First Order DE's
- [2\.1 Linear Equations](https://tutorial.math.lamar.edu/Classes/DE/Linear.aspx)
- [2\.2 Separable Equations](https://tutorial.math.lamar.edu/Classes/DE/Separable.aspx)
- [2\.3 Exact Equations](https://tutorial.math.lamar.edu/Classes/DE/Exact.aspx)
- [2\.4 Bernoulli Differential Equations](https://tutorial.math.lamar.edu/Classes/DE/Bernoulli.aspx)
- [2\.5 Substitutions](https://tutorial.math.lamar.edu/Classes/DE/Substitutions.aspx)
- [2\.6 Intervals of Validity](https://tutorial.math.lamar.edu/Classes/DE/IoV.aspx)
- [2\.7 Modeling with First Order DE's](https://tutorial.math.lamar.edu/Classes/DE/Modeling.aspx)
- [2\.8 Equilibrium Solutions](https://tutorial.math.lamar.edu/Classes/DE/EquilibriumSolutions.aspx)
- [2\.9 Euler's Method](https://tutorial.math.lamar.edu/Classes/DE/EulersMethod.aspx)
[Close submenu (3. Second Order DE's)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-32)[3\. Second Order DE's](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-32)[Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/[Differential Equations](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-32)/3\. Second Order DE's
- [3\.1 Basic Concepts](https://tutorial.math.lamar.edu/Classes/DE/SecondOrderConcepts.aspx)
- [3\.2 Real & Distinct Roots](https://tutorial.math.lamar.edu/Classes/DE/RealRoots.aspx)
- [3\.3 Complex Roots](https://tutorial.math.lamar.edu/Classes/DE/ComplexRoots.aspx)
- [3\.4 Repeated Roots](https://tutorial.math.lamar.edu/Classes/DE/RepeatedRoots.aspx)
- [3\.5 Reduction of Order](https://tutorial.math.lamar.edu/Classes/DE/ReductionofOrder.aspx)
- [3\.6 Fundamental Sets of Solutions](https://tutorial.math.lamar.edu/Classes/DE/FundamentalSetsofSolutions.aspx)
- [3\.7 More on the Wronskian](https://tutorial.math.lamar.edu/Classes/DE/Wronskian.aspx)
- [3\.8 Nonhomogeneous Differential Equations](https://tutorial.math.lamar.edu/Classes/DE/NonhomogeneousDE.aspx)
- [3\.9 Undetermined Coefficients](https://tutorial.math.lamar.edu/Classes/DE/UndeterminedCoefficients.aspx)
- [3\.10 Variation of Parameters](https://tutorial.math.lamar.edu/Classes/DE/VariationofParameters.aspx)
- [3\.11 Mechanical Vibrations](https://tutorial.math.lamar.edu/Classes/DE/Vibrations.aspx)
[Close submenu (4. Laplace Transforms)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-32)[4\. Laplace Transforms](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-32)[Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/[Differential Equations](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-32)/4\. Laplace Transforms
- [4\.1 The Definition](https://tutorial.math.lamar.edu/Classes/DE/LaplaceDefinition.aspx)
- [4\.2 Laplace Transforms](https://tutorial.math.lamar.edu/Classes/DE/LaplaceTransforms.aspx)
- [4\.3 Inverse Laplace Transforms](https://tutorial.math.lamar.edu/Classes/DE/InverseTransforms.aspx)
- [4\.4 Step Functions](https://tutorial.math.lamar.edu/Classes/DE/StepFunctions.aspx)
- [4\.5 Solving IVP's with Laplace Transforms](https://tutorial.math.lamar.edu/Classes/DE/IVPWithLaplace.aspx)
- [4\.6 Nonconstant Coefficient IVP's](https://tutorial.math.lamar.edu/Classes/DE/IVPWithNonConstantCoefficient.aspx)
- [4\.7 IVP's With Step Functions](https://tutorial.math.lamar.edu/Classes/DE/IVPWithStepFunction.aspx)
- [4\.8 Dirac Delta Function](https://tutorial.math.lamar.edu/Classes/DE/DiracDeltaFunction.aspx)
- [4\.9 Convolution Integrals](https://tutorial.math.lamar.edu/Classes/DE/ConvolutionIntegrals.aspx)
- [4\.10 Table Of Laplace Transforms](https://tutorial.math.lamar.edu/Classes/DE/Laplace_Table.aspx)
[Close submenu (5. Systems of DE's)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-32)[5\. Systems of DE's](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-32)[Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/[Differential Equations](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-32)/5\. Systems of DE's
- [5\.1 Review : Systems of Equations](https://tutorial.math.lamar.edu/Classes/DE/LA_Systems.aspx)
- [5\.2 Review : Matrices & Vectors](https://tutorial.math.lamar.edu/Classes/DE/LA_Matrix.aspx)
- [5\.3 Review : Eigenvalues & Eigenvectors](https://tutorial.math.lamar.edu/Classes/DE/LA_Eigen.aspx)
- [5\.4 Systems of Differential Equations](https://tutorial.math.lamar.edu/Classes/DE/SystemsDE.aspx)
- [5\.5 Solutions to Systems](https://tutorial.math.lamar.edu/Classes/DE/SolutionsToSystems.aspx)
- [5\.6 Phase Plane](https://tutorial.math.lamar.edu/Classes/DE/PhasePlane.aspx)
- [5\.7 Real Eigenvalues](https://tutorial.math.lamar.edu/Classes/DE/RealEigenvalues.aspx)
- [5\.8 Complex Eigenvalues](https://tutorial.math.lamar.edu/Classes/DE/ComplexEigenvalues.aspx)
- [5\.9 Repeated Eigenvalues](https://tutorial.math.lamar.edu/Classes/DE/RepeatedEigenvalues.aspx)
- [5\.10 Nonhomogeneous Systems](https://tutorial.math.lamar.edu/Classes/DE/NonhomogeneousSystems.aspx)
- [5\.11 Laplace Transforms](https://tutorial.math.lamar.edu/Classes/DE/SystemsLaplace.aspx)
- [5\.12 Modeling](https://tutorial.math.lamar.edu/Classes/DE/SystemsModeling.aspx)
[Close submenu (6. Series Solutions to DE's)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-32)[6\. Series Solutions to DE's](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-32)[Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/[Differential Equations](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-32)/6\. Series Solutions to DE's
- [6\.1 Review : Power Series](https://tutorial.math.lamar.edu/Classes/DE/PowerSeries.aspx)
- [6\.2 Review : Taylor Series](https://tutorial.math.lamar.edu/Classes/DE/TaylorSeries.aspx)
- [6\.3 Series Solutions](https://tutorial.math.lamar.edu/Classes/DE/SeriesSolutions.aspx)
- [6\.4 Euler Equations](https://tutorial.math.lamar.edu/Classes/DE/EulerEquations.aspx)
[Close submenu (7. Higher Order Differential Equations)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-32)[7\. Higher Order Differential Equations](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-32)[Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/[Differential Equations](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-32)/7\. Higher Order Differential Equations
- [7\.1 Basic Concepts for *n*th Order Linear Equations](https://tutorial.math.lamar.edu/Classes/DE/HOBasicConcepts.aspx)
- [7\.2 Linear Homogeneous Differential Equations](https://tutorial.math.lamar.edu/Classes/DE/HOHomogeneousDE.aspx)
- [7\.3 Undetermined Coefficients](https://tutorial.math.lamar.edu/Classes/DE/HOUndeterminedCoeff.aspx)
- [7\.4 Variation of Parameters](https://tutorial.math.lamar.edu/Classes/DE/HOVariationOfParam.aspx)
- [7\.5 Laplace Transforms](https://tutorial.math.lamar.edu/Classes/DE/HOLaplaceTransforms.aspx)
- [7\.6 Systems of Differential Equations](https://tutorial.math.lamar.edu/Classes/DE/HOSystems.aspx)
- [7\.7 Series Solutions](https://tutorial.math.lamar.edu/Classes/DE/HOSeries.aspx)
[Close submenu (8. Boundary Value Problems & Fourier Series)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-32)[8\. Boundary Value Problems & Fourier Series](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-32)[Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/[Differential Equations](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-32)/8\. Boundary Value Problems & Fourier Series
- [8\.1 Boundary Value Problems](https://tutorial.math.lamar.edu/Classes/DE/BoundaryValueProblem.aspx)
- [8\.2 Eigenvalues and Eigenfunctions](https://tutorial.math.lamar.edu/Classes/DE/BVPEvals.aspx)
- [8\.3 Periodic Functions & Orthogonal Functions](https://tutorial.math.lamar.edu/Classes/DE/PeriodicOrthogonal.aspx)
- [8\.4 Fourier Sine Series](https://tutorial.math.lamar.edu/Classes/DE/FourierSineSeries.aspx)
- [8\.5 Fourier Cosine Series](https://tutorial.math.lamar.edu/Classes/DE/FourierCosineSeries.aspx)
- [8\.6 Fourier Series](https://tutorial.math.lamar.edu/Classes/DE/FourierSeries.aspx)
- [8\.7 Convergence of Fourier Series](https://tutorial.math.lamar.edu/Classes/DE/ConvergenceFourierSeries.aspx)
[Close submenu (9. Partial Differential Equations )](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-32)[9\. Partial Differential Equations](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-32) [Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/[Differential Equations](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-32)/9\. Partial Differential Equations
- [9\.1 The Heat Equation](https://tutorial.math.lamar.edu/Classes/DE/TheHeatEquation.aspx)
- [9\.2 The Wave Equation](https://tutorial.math.lamar.edu/Classes/DE/TheWaveEquation.aspx)
- [9\.3 Terminology](https://tutorial.math.lamar.edu/Classes/DE/PDETerminology.aspx)
- [9\.4 Separation of Variables](https://tutorial.math.lamar.edu/Classes/DE/SeparationofVariables.aspx)
- [9\.5 Solving the Heat Equation](https://tutorial.math.lamar.edu/Classes/DE/SolvingHeatEquation.aspx)
- [9\.6 Heat Equation with Non-Zero Temperature Boundaries](https://tutorial.math.lamar.edu/Classes/DE/HeatEqnNonZero.aspx)
- [9\.7 Laplace's Equation](https://tutorial.math.lamar.edu/Classes/DE/LaplacesEqn.aspx)
- [9\.8 Vibrating String](https://tutorial.math.lamar.edu/Classes/DE/VibratingString.aspx)
- [9\.9 Summary of Separation of Variables](https://tutorial.math.lamar.edu/Classes/DE/PDESummary.aspx)
[Close submenu (Algebra & Trig Review)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)[Algebra & Trig Review](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)[Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/Algebra & Trig Review
- [Open submenu (1. Algebra)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-43)[1\. Algebra](https://tutorial.math.lamar.edu/Extras/AlgebraTrigReview/AlgebraIntro.aspx)
- [Open submenu (2. Trigonometry)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-44)[2\. Trigonometry](https://tutorial.math.lamar.edu/Extras/AlgebraTrigReview/TrigIntro.aspx)
- [Open submenu (3. Exponentials & Logarithms)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-45)[3\. Exponentials & Logarithms](https://tutorial.math.lamar.edu/Extras/AlgebraTrigReview/ExpLogIntro.aspx)
[Close submenu (1. Algebra)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-42)[1\. Algebra](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-42)[Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/[Algebra & Trig Review](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-42)/1\. Algebra
- [1\.1 Exponents](https://tutorial.math.lamar.edu/Extras/AlgebraTrigReview/Exponents.aspx)
- [1\.2 Absolute Value](https://tutorial.math.lamar.edu/Extras/AlgebraTrigReview/AbsoluteValue.aspx)
- [1\.3 Radicals](https://tutorial.math.lamar.edu/Extras/AlgebraTrigReview/Radicals.aspx)
- [1\.4 Rationalizing](https://tutorial.math.lamar.edu/Extras/AlgebraTrigReview/Rationalizing.aspx)
- [1\.5 Functions](https://tutorial.math.lamar.edu/Extras/AlgebraTrigReview/Functions.aspx)
- [1\.6 Multiplying Polynomials](https://tutorial.math.lamar.edu/Extras/AlgebraTrigReview/MultPoly.aspx)
- [1\.7 Factoring](https://tutorial.math.lamar.edu/Extras/AlgebraTrigReview/Factoring.aspx)
- [1\.8 Simplifying Rational Expressions](https://tutorial.math.lamar.edu/Extras/AlgebraTrigReview/SimpRatExp.aspx)
- [1\.9 Graphing and Common Graphs](https://tutorial.math.lamar.edu/Extras/AlgebraTrigReview/Graphing.aspx)
- [1\.10 Solving Equations, Part I](https://tutorial.math.lamar.edu/Extras/AlgebraTrigReview/SolveEqnPtI.aspx)
- [1\.11 Solving Equations, Part II](https://tutorial.math.lamar.edu/Extras/AlgebraTrigReview/SolveEqnPtII.aspx)
- [1\.12 Solving Systems of Equations](https://tutorial.math.lamar.edu/Extras/AlgebraTrigReview/SolveSystems.aspx)
- [1\.13 Solving Inequalities](https://tutorial.math.lamar.edu/Extras/AlgebraTrigReview/SolveIneq.aspx)
- [1\.14 Absolute Value Equations and Inequalities](https://tutorial.math.lamar.edu/Extras/AlgebraTrigReview/SolveAbsValue.aspx)
[Close submenu (2. Trigonometry)](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-42)[2\. Trigonometry](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-42)[Pauls Notes](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-1)/[Algebra & Trig Review](https://tutorial.math.lamar.edu/classes/de/inversetransforms.aspx#mm-42)/2\. Trigonometry
- [2\.1 Trig Function Evaluation](https://tutorial.math.lamar.edu/Extras/AlgebraTrigReview/TrigFunctions.aspx)
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### Section 4.3 : Inverse Laplace Transforms
Finding the Laplace transform of a function is not terribly difficult if we’ve got a table of transforms in front of us to use as we saw in the last [section](https://tutorial.math.lamar.edu/classes/de/LaplaceTransforms.aspx). What we would like to do now is go the other way.
We are going to be given a transform, F(s) F ( s ), and ask what function (or functions) did we have originally. As you will see this can be a more complicated and lengthy process than taking transforms. In these cases we say that we are finding the **Inverse Laplace Transform** of F(s) F ( s ) and use the following notation.
f(t)\=L−1{F(s)}
f
(
t
)
\=
L
−
1
{
F
(
s
)
}
As with Laplace transforms, we’ve got the following fact to help us take the inverse transform.
#### Fact
Given the two Laplace transforms F(s) F ( s ) and G(s) G ( s ) then
L−1{aF(s)\+bG(s)}\=aL−1{F(s)}\+bL−1{G(s)}
L
−
1
{
a
F
(
s
)
\+
b
G
(
s
)
}
\=
a
L
−
1
{
F
(
s
)
}
\+
b
L
−
1
{
G
(
s
)
}
for any constants a a and b b.
So, we take the inverse transform of the individual transforms, put any constants back in and then add or subtract the results back up.
Let’s take a look at a couple of fairly simple inverse transforms.
Example 1 Find the inverse transform of each of the following.
1. F(s)\=6s−1s−8\+4s−3
F
(
s
)
\=
6
s
−
1
s
−
8
\+
4
s
−
3
2. H(s)\=19s\+2−13s−5\+7s5
H
(
s
)
\=
19
s
\+
2
−
1
3
s
−
5
\+
7
s
5
3. F(s)\=6ss2\+25\+3s2\+25
F
(
s
)
\=
6
s
s
2
\+
25
\+
3
s
2
\+
25
4. G(s)\=83s2\+12\+3s2−49
G
(
s
)
\=
8
3
s
2
\+
12
\+
3
s
2
−
49
Show All Solutions Hide All Solutions
Show Discussion
We’ve always felt that the key to doing inverse transforms is to look at the denominator and try to identify what you’ve got based on that. If there is only one entry in the table that has that particular denominator, the next step is to make sure the numerator is correctly set up for the inverse transform process. If it isn’t, correct it (this is always easy to do) and then take the inverse transform.
If there is more than one entry in the table that has a particular denominator, then the numerators of each will be different, so go up to the numerator and see which one you’ve got. If you need to correct the numerator to get it into the correct form and then take the inverse transform.
So, with this advice in mind let’s see if we can take some inverse transforms.
a
F(s)\=6s−1s−8\+4s−3
F
(
s
)
\=
6
s
−
1
s
−
8
\+
4
s
−
3
Show Solution
From the denominator of the first term it looks like the first term is just a constant. The correct numerator for this term is a “1” so we’ll just factor the 6 out before taking the inverse transform. The second term appears to be an exponential with a\=8 a \= 8 and the numerator is exactly what it needs to be. The third term also appears to be an exponential, only this time a\=3 a \= 3 and we’ll need to factor the 4 out before taking the inverse transforms.
So, with a little more detail than we’ll usually put into these,
F(s)\=61s−1s−8\+41s−3f(t)\=6(1)−e8t\+4(e3t)\=6−e8t\+4e3t
F
(
s
)
\=
6
1
s
−
1
s
−
8
\+
4
1
s
−
3
f
(
t
)
\=
6
(
1
)
−
e
8
t
\+
4
(
e
3
t
)
\=
6
−
e
8
t
\+
4
e
3
t
b
H(s)\=19s\+2−13s−5\+7s5
H
(
s
)
\=
19
s
\+
2
−
1
3
s
−
5
\+
7
s
5
Show Solution
The first term in this case looks like an exponential with a\=−2 a \= − 2 and we’ll need to factor out the 19. Be careful with negative signs in these problems, it’s very easy to lose track of them.
The second term almost looks like an exponential, except that it’s got a 3s 3 s instead of just an s s in the denominator. It is an exponential, but in this case, we’ll need to factor a 3 out of the denominator before taking the inverse transform.
The denominator of the third term appears to be [\#3](https://tutorial.math.lamar.edu/classes/de/Laplace_Table.aspx#LT_3) in the table with n\=4 n \= 4. The numerator however, is not correct for this. There is currently a 7 in the numerator and we need a 4\!\=24 4 \! \= 24 in the numerator. This is very easy to fix. Whenever a numerator is off by a multiplicative constant, as in this case, all we need to do is put the constant that we need in the numerator. We will just need to remember to take it back out by dividing by the same constant.
So, let’s first rewrite the transform.
H(s)\=19s−(−2)−13(s−53)\+74\!4\!s4\+1\=191s−(−2)−131s−53\+74\!4\!s4\+1
H
(
s
)
\=
19
s
−
(
−
2
)
−
1
3
(
s
−
5
3
)
\+
7
4
\!
4
\!
s
4
\+
1
\=
19
1
s
−
(
−
2
)
−
1
3
1
s
−
5
3
\+
7
4
\!
4
\!
s
4
\+
1
So, what did we do here? We factored the 19 out of the first term. We factored the 3 out of the denominator of the second term since it can’t be there for the inverse transform and in the third term we factored everything out of the numerator except the 4! since that is the portion that we need in the numerator for the inverse transform process.
Let’s now take the inverse transform.
h(t)\=19e−2t−13e5t3\+724t4
h
(
t
)
\=
19
e
−
2
t
−
1
3
e
5
t
3
\+
7
24
t
4
c
F(s)\=6ss2\+25\+3s2\+25
F
(
s
)
\=
6
s
s
2
\+
25
\+
3
s
2
\+
25
Show Solution
In this part we’ve got the same denominator in both terms and our table tells us that we’ve either got [\#7](https://tutorial.math.lamar.edu/classes/de/Laplace_Table.aspx#LT_7) or [\#8](https://tutorial.math.lamar.edu/classes/de/Laplace_Table.aspx#LT_8). The numerators will tell us which we’ve actually got. The first one has an s s in the numerator and so this means that the first term must be \#8 and we’ll need to factor the 6 out of the numerator in this case. The second term has only a constant in the numerator and so this term must be \#7, however, in order for this to be exactly \#7 we’ll need to multiply/divide a 5 in the numerator to get it correct for the table.
The transform becomes,
F(s)\=6ss2\+(5)2\+355s2\+(5)2\=6ss2\+(5)2\+355s2\+(5)2
F
(
s
)
\=
6
s
s
2
\+
(
5
)
2
\+
3
5
5
s
2
\+
(
5
)
2
\=
6
s
s
2
\+
(
5
)
2
\+
3
5
5
s
2
\+
(
5
)
2
Taking the inverse transform gives,
f(t)\=6cos(5t)\+35sin(5t)
f
(
t
)
\=
6
cos
(
5
t
)
\+
3
5
sin
(
5
t
)
d
G(s)\=83s2\+12\+3s2−49
G
(
s
)
\=
8
3
s
2
\+
12
\+
3
s
2
−
49
Show Solution
In this case the first term will be a sine once we factor a 3 out of the denominator, while the second term appears to be a hyperbolic sine ([\#17](https://tutorial.math.lamar.edu/classes/de/Laplace_Table.aspx#LT_17)). Again, be careful with the difference between these two. Both of the terms will also need to have their numerators fixed up. Here is the transform once we’re done rewriting it.
G(s)\=138s2\+4\+3s2−49\=13(4)(2)s2\+(2)2\+377s2−(7)2
G
(
s
)
\=
1
3
8
s
2
\+
4
\+
3
s
2
−
49
\=
1
3
(
4
)
(
2
)
s
2
\+
(
2
)
2
\+
3
7
7
s
2
−
(
7
)
2
Notice that in the first term we took advantage of the fact that we could get the 2 in the numerator that we needed by factoring the 8. The inverse transform is then,
g(t)\=43sin(2t)\+37sinh(7t)
g
(
t
)
\=
4
3
sin
(
2
t
)
\+
3
7
sinh
(
7
t
)
So, probably the best way to identify the transform is by looking at the denominator. If there is more than one possibility use the numerator to identify the correct one. Fix up the numerator if needed to get it into the form needed for the inverse transform process. Finally, take the inverse transform.
Let’s do some slightly harder problems. These are a little more involved than the first set.
Example 2 Find the inverse transform of each of the following.
1. F(s)\=6s−5s2\+7
F
(
s
)
\=
6
s
−
5
s
2
\+
7
2. F(s)\=1−3ss2\+8s\+21
F
(
s
)
\=
1
−
3
s
s
2
\+
8
s
\+
21
3. G(s)\=3s−22s2−6s−2
G
(
s
)
\=
3
s
−
2
2
s
2
−
6
s
−
2
4. H(s)\=s\+7s2−3s−10
H
(
s
)
\=
s
\+
7
s
2
−
3
s
−
10
Show All Solutions Hide All Solutions
a
F(s)\=6s−5s2\+7
F
(
s
)
\=
6
s
−
5
s
2
\+
7
Show Solution
From the denominator of this one it appears that it is either a sine or a cosine. However, the numerator doesn’t match up to either of these in the table. A cosine wants just an s s in the numerator with at most a multiplicative constant, while a sine wants only a constant and no s s in the numerator.
We’ve got both in the numerator. This is easy to fix however. We will just split up the transform into two terms and then do inverse transforms.
F(s)\=6ss2\+7−5√7√7s2\+7f(t)\=6cos(√7t)−5√7sin(√7t)
F
(
s
)
\=
6
s
s
2
\+
7
−
5
7
7
s
2
\+
7
f
(
t
)
\=
6
cos
(
7
t
)
−
5
7
sin
(
7
t
)
Do not get too used to always getting the perfect squares in sines and cosines that we saw in the first set of examples. More often than not (at least in my class) they won’t be perfect squares\!
b
F(s)\=1−3ss2\+8s\+21
F
(
s
)
\=
1
−
3
s
s
2
\+
8
s
\+
21
Show Solution
In this case there are no denominators in our table that look like this. We can however make the denominator look like one of the denominators in the table by completing the square on the denominator. So, let’s do that first.
s2\+8s\+21\=s2\+8s\+16−16\+21\=s2\+8s\+16\+5\=(s\+4)2\+5
s
2
\+
8
s
\+
21
\=
s
2
\+
8
s
\+
16
−
16
\+
21
\=
s
2
\+
8
s
\+
16
\+
5
\=
(
s
\+
4
)
2
\+
5
Recall that in completing the square you take half the coefficient of the s s, square this, and then add and subtract the result to the polynomial. After doing this the first three terms should factor as a perfect square.
So, the transform can be written as the following.
F(s)\=1−3s(s\+4)2\+5
F
(
s
)
\=
1
−
3
s
(
s
\+
4
)
2
\+
5
Okay, with this rewrite it looks like we’ve got [\#19](https://tutorial.math.lamar.edu/classes/de/Laplace_Table.aspx#LT_19) and/or [\#20](https://tutorial.math.lamar.edu/classes/de/Laplace_Table.aspx#LT_20)’s from our table of transforms. However, note that in order for it to be a [\#19](https://tutorial.math.lamar.edu/classes/de/Laplace_Table.aspx) we want just a constant in the numerator and in order to be a [\#20](https://tutorial.math.lamar.edu/classes/de/Laplace_Table.aspx) we need an s–a s – a in the numerator. We’ve got neither of these, so we’ll have to correct the numerator to get it into proper form.
In correcting the numerator always get the s–a s – a first. This is the important part. We will also need to be careful of the 3 that sits in front of the s s. One way to take care of this is to break the term into two pieces, factor the 3 out of the second and then fix up the numerator of this term. This will work; however, it will put three terms into our answer and there are really only two terms.
So, we will leave the transform as a single term and correct it as follows,
F(s)\=1−3(s\+4−4)(s\+4)2\+5\=1−3(s\+4)\+12(s\+4)2\+5\=−3(s\+4)\+13(s\+4)2\+5
F
(
s
)
\=
1
−
3
(
s
\+
4
−
4
)
(
s
\+
4
)
2
\+
5
\=
1
−
3
(
s
\+
4
)
\+
12
(
s
\+
4
)
2
\+
5
\=
−
3
(
s
\+
4
)
\+
13
(
s
\+
4
)
2
\+
5
We needed an s\+4 s \+ 4 in the numerator, so we put that in. We just needed to make sure and take the 4 back out by subtracting it back out. Also, because of the 3 multiplying the s s we needed to do all this inside a set of parenthesis. Then we partially multiplied the 3 through the second term and combined the constants. With the transform in this form, we can break it up into two transforms each of which are in the tables and so we can do inverse transforms on them,
F(s)\=−3s\+4(s\+4)2\+5\+13√5√5(s\+4)2\+5f(t)\=−3e−4tcos(√5t)\+13√5e−4tsin(√5t)
F
(
s
)
\=
−
3
s
\+
4
(
s
\+
4
)
2
\+
5
\+
13
5
5
(
s
\+
4
)
2
\+
5
f
(
t
)
\=
−
3
e
−
4
t
cos
(
5
t
)
\+
13
5
e
−
4
t
sin
(
5
t
)
c
G(s)\=3s−22s2−6s−2
G
(
s
)
\=
3
s
−
2
2
s
2
−
6
s
−
2
Show Solution
This one is similar to the last one. We just need to be careful with the completing the square however. The first thing that we should do is factor a 2 out of the denominator, then complete the square. Remember that when completing the square a coefficient of 1 on the s2 s 2 term is needed! So, here’s the work for this transform.
G(s)\=3s−22(s2−3s−1)\=123s−2s2−3s\+94−94−1\=123s−2(s−32)2−134
G
(
s
)
\=
3
s
−
2
2
(
s
2
−
3
s
−
1
)
\=
1
2
3
s
−
2
s
2
−
3
s
\+
9
4
−
9
4
−
1
\=
1
2
3
s
−
2
(
s
−
3
2
)
2
−
13
4
So, it looks like we’ve got [\#21](https://tutorial.math.lamar.edu/classes/de/Laplace_Table.aspx#LT_21) and [\#22](https://tutorial.math.lamar.edu/classes/de/Laplace_Table.aspx#LT_22) with a corrected numerator. Here’s the work for that and the inverse transform.
G(s)\=123(s−32\+32)−2(s−32)2−134\=123(s−32)\+52(s−32)2−134\=12⎛⎜ ⎜⎝3(s−32)(s−32)2−134\+52√13√13(s−32)2−134⎞⎟ ⎟⎠g(t)\=12(3e3t2cosh(√132t)\+5√13e3t2sinh(√132t))
G
(
s
)
\=
1
2
3
(
s
−
3
2
\+
3
2
)
−
2
(
s
−
3
2
)
2
−
13
4
\=
1
2
3
(
s
−
3
2
)
\+
5
2
(
s
−
3
2
)
2
−
13
4
\=
1
2
(
3
(
s
−
3
2
)
(
s
−
3
2
)
2
−
13
4
\+
5
2
13
13
(
s
−
3
2
)
2
−
13
4
)
g
(
t
)
\=
1
2
(
3
e
3
t
2
cosh
(
13
2
t
)
\+
5
13
e
3
t
2
sinh
(
13
2
t
)
)
In correcting the numerator of the second term, notice that I only put in the square root since we already had the “over 2” part of the fraction that we needed in the numerator.
d
H(s)\=s\+7s2−3s−10
H
(
s
)
\=
s
\+
7
s
2
−
3
s
−
10
Show Solution
This one appears to be similar to the previous two, but it actually isn’t. The denominators in the previous two couldn’t be easily factored. In this case the denominator does factor and so we need to deal with it differently. Here is the transform with the factored denominator.
H(s)\=s\+7(s\+2)(s−5)
H
(
s
)
\=
s
\+
7
(
s
\+
2
)
(
s
−
5
)
The denominator of this transform seems to suggest that we’ve got a couple of exponentials, however in order to be exponentials there can only be a single term in the denominator and no s s’s in the numerator.
To fix this we will need to do partial fractions on this transform. In this case the partial fraction decomposition will be
H(s)\=As\+2\+Bs−5
H
(
s
)
\=
A
s
\+
2
\+
B
s
−
5
Don’t remember how to do partial fractions? In this example we’ll show you one way of getting the values of the constants and after this example we’ll review how to get the correct form of the partial fraction decomposition.
Okay, so let’s get the constants. There is a method for finding the constants that will always work, however it can lead to more work than is sometimes required. Eventually, we will need that method, however in this case there is an easier way to find the constants.
Regardless of the method used, the first step is to actually add the two terms back up. This gives the following.
s\+7(s\+2)(s−5)\=A(s−5)\+B(s\+2)(s\+2)(s−5)
s
\+
7
(
s
\+
2
)
(
s
−
5
)
\=
A
(
s
−
5
)
\+
B
(
s
\+
2
)
(
s
\+
2
)
(
s
−
5
)
Now, this needs to be true for any s s that we should choose to put in. So, since the denominators are the same we just need to get the numerators equal. Therefore, set the numerators equal.
s\+7\=A(s−5)\+B(s\+2)
s
\+
7
\=
A
(
s
−
5
)
\+
B
(
s
\+
2
)
Again, this must be true for ANY value of s s that we want to put in. So, let’s take advantage of that. If it must be true for any value of s s then it must be true for s\=−2 s \= − 2, to pick a value at random. In this case we get,
5\=A(−7)\+B(0)⇒A\=−57
5
\=
A
(
−
7
)
\+
B
(
0
)
⇒
A
\=
−
5
7
We found A A by appropriately picking s s. We can B B in the same way if we chose s\=5 s \= 5.
12\=A(0)\+B(7)⇒B\=127
12
\=
A
(
0
)
\+
B
(
7
)
⇒
B
\=
12
7
This will not always work, but when it does it will usually simplify the work considerably.
So, with these constants the transform becomes,
H(s)\=−57s\+2\+127s−5
H
(
s
)
\=
−
5
7
s
\+
2
\+
12
7
s
−
5
We can now easily do the inverse transform to get,
h(t)\=−57e−2t\+127e5t
h
(
t
)
\=
−
5
7
e
−
2
t
\+
12
7
e
5
t
The last part of this example needed partial fractions to get the inverse transform. When we finally get back to differential equations and we start using Laplace transforms to solve them, you will quickly come to understand that partial fractions are a fact of life in these problems. Almost every problem will require partial fractions to one degree or another.
Note that we could have done the last part of this example as we had done the previous two parts. If we had we would have gotten hyperbolic functions. However, recalling the [definition](https://tutorial.math.lamar.edu/classes/de/Laplace_Table.aspx#Note2) of the hyperbolic functions we could have written the result in the form we got from the way we worked our problem. However, most students have a better feel for exponentials than they do for hyperbolic functions and so it’s usually best to just use partial fractions and get the answer in terms of exponentials. It may be a little more work, but it will give a nicer (and easier to work with) form of the answer.
Be warned that in my class I’ve got a rule that if the denominator can be factored with integer coefficients then it must be.
So, let’s remind you how to get the correct partial fraction decomposition. The first step is to factor the denominator as much as possible. Then for each term in the denominator we will use the following table to get a term or terms for our partial fraction decomposition.
| Factor in denominator | Term in partial fraction decomposition |
|---|---|
| ax\+b a x \+ b | |
Notice that the first and third cases are really special cases of the second and fourth cases respectively.
So, let’s do a couple more examples to remind you how to do partial fractions.
Example 3 Find the inverse transform of each of the following.
1. G(s)\=86s−78(s\+3)(s−4)(5s−1)
G
(
s
)
\=
86
s
−
78
(
s
\+
3
)
(
s
−
4
)
(
5
s
−
1
)
2. F(s)\=2−5s(s−6)(s2\+11)
F
(
s
)
\=
2
−
5
s
(
s
−
6
)
(
s
2
\+
11
)
3. G(s)\=25s3(s2\+4s\+5)
G
(
s
)
\=
25
s
3
(
s
2
\+
4
s
\+
5
)
Show All Solutions Hide All Solutions
a
G(s)\=86s−78(s\+3)(s−4)(5s−1)
G
(
s
)
\=
86
s
−
78
(
s
\+
3
)
(
s
−
4
)
(
5
s
−
1
)
Show Solution
Here’s the partial fraction decomposition for this part.
G(s)\=As\+3\+Bs−4\+C5s−1
G
(
s
)
\=
A
s
\+
3
\+
B
s
−
4
\+
C
5
s
−
1
Now, this time we won’t go into quite the detail as we did in the last example. We are after the numerator of the partial fraction decomposition and this is usually easy enough to do in our heads. Therefore, we will go straight to setting numerators equal.
86s−78\=A(s−4)(5s−1)\+B(s\+3)(5s−1)\+C(s\+3)(s−4)
86
s
−
78
\=
A
(
s
−
4
)
(
5
s
−
1
)
\+
B
(
s
\+
3
)
(
5
s
−
1
)
\+
C
(
s
\+
3
)
(
s
−
4
)
As with the last example, we can easily get the constants by correctly picking values of s s.
s\=−3−336\=A(−7)(−16)⇒A\=−3s\=15−3045\=C(165)(−195)⇒C\=5s\=4266\=B(7)(19)⇒B\=2
s
\=
−
3
−
336
\=
A
(
−
7
)
(
−
16
)
⇒
A
\=
−
3
s
\=
1
5
−
304
5
\=
C
(
16
5
)
(
−
19
5
)
⇒
C
\=
5
s
\=
4
266
\=
B
(
7
)
(
19
)
⇒
B
\=
2
So, the partial fraction decomposition for this transform is,
G(s)\=−3s\+3\+2s−4\+55s−1
G
(
s
)
\=
−
3
s
\+
3
\+
2
s
−
4
\+
5
5
s
−
1
Now, in order to actually take the inverse transform we will need to factor a 5 out of the denominator of the last term. The corrected transform as well as its inverse transform is.
G(s)\=−3s\+3\+2s−4\+1s−15g(t)\=−3e−3t\+2e4t\+et5
G
(
s
)
\=
−
3
s
\+
3
\+
2
s
−
4
\+
1
s
−
1
5
g
(
t
)
\=
−
3
e
−
3
t
\+
2
e
4
t
\+
e
t
5
b
F(s)\=2−5s(s−6)(s2\+11)
F
(
s
)
\=
2
−
5
s
(
s
−
6
)
(
s
2
\+
11
)
Show Solution
So, for the first time we’ve got a quadratic in the denominator. Here’s the decomposition for this part.
F(s)\=As−6\+Bs\+Cs2\+11
F
(
s
)
\=
A
s
−
6
\+
B
s
\+
C
s
2
\+
11
Setting numerators equal gives,
2−5s\=A(s2\+11)\+(Bs\+C)(s−6)
2
−
5
s
\=
A
(
s
2
\+
11
)
\+
(
B
s
\+
C
)
(
s
−
6
)
Okay, in this case we could use s\=6 s \= 6 to quickly find A A, but that’s all it would give. In this case we will need to go the “long” way around to getting the constants. Note that this way will always work but is sometimes more work than is required.
The “long” way is to completely multiply out the right side and collect like terms.
2−5s\=A(s2\+11)\+(Bs\+C)(s−6)\=As2\+11A\+Bs2−6Bs\+Cs−6C\=(A\+B)s2\+(−6B\+C)s\+11A−6C
2
−
5
s
\=
A
(
s
2
\+
11
)
\+
(
B
s
\+
C
)
(
s
−
6
)
\=
A
s
2
\+
11
A
\+
B
s
2
−
6
B
s
\+
C
s
−
6
C
\=
(
A
\+
B
)
s
2
\+
(
−
6
B
\+
C
)
s
\+
11
A
−
6
C
In order for these two to be equal the coefficients of the s2 s 2, s s and the constants must all be equal. So, setting coefficients equal gives the following system of equations that can be solved.
s2:A\+B\=0s1:−6B\+C\=−5s0:11A−6C\=2⎫⎪⎬⎪⎭⇒A\=−2847,B\=2847,C\=−6747
s
2
:
A
\+
B
\=
0
s
1
:
−
6
B
\+
C
\=
−
5
s
0
:
11
A
−
6
C
\=
2
}
⇒
A
\=
−
28
47
,
B
\=
28
47
,
C
\=
−
67
47
Notice that we used s0 s 0 to denote the constants. This is habit on my part and isn’t really required, it’s just what I’m used to doing. Also, the coefficients are fairly messy fractions in this case. Get used to that. They will often be like this when we get back into solving differential equations.
There is a way to make our life a little easier as well with this. Since all of the fractions have a denominator of 47 we’ll factor that out as we plug them back into the decomposition. This will make dealing with them much easier. The partial fraction decomposition is then,
F(s)\=147(−28s−6\+28s−67s2\+11)\=147⎛⎜ ⎜⎝−28s−6\+28ss2\+11−67√11√11s2\+11⎞⎟ ⎟⎠
F
(
s
)
\=
1
47
(
−
28
s
−
6
\+
28
s
−
67
s
2
\+
11
)
\=
1
47
(
−
28
s
−
6
\+
28
s
s
2
\+
11
−
67
11
11
s
2
\+
11
)
The inverse transform is then.
f(t)\=147(−28e6t\+28cos(√11t)−67√11sin(√11t))
f
(
t
)
\=
1
47
(
−
28
e
6
t
\+
28
cos
(
11
t
)
−
67
11
sin
(
11
t
)
)
c
G(s)\=25s3(s2\+4s\+5)
G
(
s
)
\=
25
s
3
(
s
2
\+
4
s
\+
5
)
Show Solution
With this last part do not get excited about the s3 s 3. We can think of this term as
s3\=(s−0)3
s
3
\=
(
s
−
0
)
3
and it becomes a linear term to a power. So, the partial fraction decomposition is
G(s)\=As\+Bs2\+Cs3\+Ds\+Es2\+4s\+5
G
(
s
)
\=
A
s
\+
B
s
2
\+
C
s
3
\+
D
s
\+
E
s
2
\+
4
s
\+
5
Setting numerators equal and multiplying out gives.
25\=As2(s2\+4s\+5)\+Bs(s2\+4s\+5)\+C(s2\+4s\+5)\+(Ds\+E)s3\=(A\+D)s4\+(4A\+B\+E)s3\+(5A\+4B\+C)s2\+(5B\+4C)s\+5C
25
\=
A
s
2
(
s
2
\+
4
s
\+
5
)
\+
B
s
(
s
2
\+
4
s
\+
5
)
\+
C
(
s
2
\+
4
s
\+
5
)
\+
(
D
s
\+
E
)
s
3
\=
(
A
\+
D
)
s
4
\+
(
4
A
\+
B
\+
E
)
s
3
\+
(
5
A
\+
4
B
\+
C
)
s
2
\+
(
5
B
\+
4
C
)
s
\+
5
C
Setting coefficients equal gives the following system.
s4:A\+D\=0s3:4A\+B\+E\=0s2:5A\+4B\+C\=0s1:5B\+4C\=0s0:5C\=25⎫⎪ ⎪ ⎪ ⎪ ⎪ ⎪⎬⎪ ⎪ ⎪ ⎪ ⎪ ⎪⎭⇒A\=115,B\=−4,C\=5,D\=−115,E\=−245
s
4
:
A
\+
D
\=
0
s
3
:
4
A
\+
B
\+
E
\=
0
s
2
:
5
A
\+
4
B
\+
C
\=
0
s
1
:
5
B
\+
4
C
\=
0
s
0
:
5
C
\=
25
}
⇒
A
\=
11
5
,
B
\=
−
4
,
C
\=
5
,
D
\=
−
11
5
,
E
\=
−
24
5
This system looks messy, but it’s easier to solve than it might look. First, we get C C for free from the last equation. We can then use the fourth equation to find B B. The third equation will then give A A, *etc*.
When plugging into the decomposition we’ll get everything with a denominator of 5, then factor that out as we did in the previous part in order to make things easier to deal with.
G(s)\=15(11s−20s2\+25s3−11s\+24s2\+4s\+5)
G
(
s
)
\=
1
5
(
11
s
−
20
s
2
\+
25
s
3
−
11
s
\+
24
s
2
\+
4
s
\+
5
)
Note that we also factored a minus sign out of the last two terms. To complete this part we’ll need to complete the square on the later term and fix up a couple of numerators. Here’s that work.
G(s)\=15(11s−20s2\+25s3−11s\+24s2\+4s\+5)\=15(11s−20s2\+25s3−11(s\+2−2)\+24(s\+2)2\+1)\=15(11s−20s2\+252\!2\!s3−11(s\+2)(s\+2)2\+1−2(s\+2)2\+1)
G
(
s
)
\=
1
5
(
11
s
−
20
s
2
\+
25
s
3
−
11
s
\+
24
s
2
\+
4
s
\+
5
)
\=
1
5
(
11
s
−
20
s
2
\+
25
s
3
−
11
(
s
\+
2
−
2
)
\+
24
(
s
\+
2
)
2
\+
1
)
\=
1
5
(
11
s
−
20
s
2
\+
25
2
\!
2
\!
s
3
−
11
(
s
\+
2
)
(
s
\+
2
)
2
\+
1
−
2
(
s
\+
2
)
2
\+
1
)
The inverse transform is then.
g(t)\=15(11−20t\+252t2−11e−2tcos(t)−2e−2tsin(t))
g
(
t
)
\=
1
5
(
11
−
20
t
\+
25
2
t
2
−
11
e
−
2
t
cos
(
t
)
−
2
e
−
2
t
sin
(
t
)
)
So, one final time. Partial fractions are a fact of life when using Laplace transforms to solve differential equations. Make sure that you can deal with them.
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### Section 4.3 : Inverse Laplace Transforms
Finding the Laplace transform of a function is not terribly difficult if we’ve got a table of transforms in front of us to use as we saw in the last [section](https://tutorial.math.lamar.edu/classes/de/LaplaceTransforms.aspx). What we would like to do now is go the other way.
We are going to be given a transform, F ( s ), and ask what function (or functions) did we have originally. As you will see this can be a more complicated and lengthy process than taking transforms. In these cases we say that we are finding the **Inverse Laplace Transform** of F ( s ) and use the following notation.
f ( t ) \= L − 1 { F ( s ) }
As with Laplace transforms, we’ve got the following fact to help us take the inverse transform.
#### Fact
Given the two Laplace transforms F ( s ) and G ( s ) then
L − 1 { a F ( s ) \+ b G ( s ) } \= a L − 1 { F ( s ) } \+ b L − 1 { G ( s ) }
for any constants a and b.
So, we take the inverse transform of the individual transforms, put any constants back in and then add or subtract the results back up.
Let’s take a look at a couple of fairly simple inverse transforms.
Example 1 Find the inverse transform of each of the following.
1. F
(
s
)
\=
6
s
−
1
s
−
8
\+
4
s
−
3
2. H
(
s
)
\=
19
s
\+
2
−
1
3
s
−
5
\+
7
s
5
3. F
(
s
)
\=
6
s
s
2
\+
25
\+
3
s
2
\+
25
4. G
(
s
)
\=
8
3
s
2
\+
12
\+
3
s
2
−
49
Show All Solutions Hide All Solutions
Show Discussion
We’ve always felt that the key to doing inverse transforms is to look at the denominator and try to identify what you’ve got based on that. If there is only one entry in the table that has that particular denominator, the next step is to make sure the numerator is correctly set up for the inverse transform process. If it isn’t, correct it (this is always easy to do) and then take the inverse transform.
If there is more than one entry in the table that has a particular denominator, then the numerators of each will be different, so go up to the numerator and see which one you’ve got. If you need to correct the numerator to get it into the correct form and then take the inverse transform.
So, with this advice in mind let’s see if we can take some inverse transforms.
a F ( s ) \= 6 s − 1 s − 8 \+ 4 s − 3 Show Solution
From the denominator of the first term it looks like the first term is just a constant. The correct numerator for this term is a “1” so we’ll just factor the 6 out before taking the inverse transform. The second term appears to be an exponential with a \= 8 and the numerator is exactly what it needs to be. The third term also appears to be an exponential, only this time a \= 3 and we’ll need to factor the 4 out before taking the inverse transforms.
So, with a little more detail than we’ll usually put into these,
F ( s ) \= 6 1 s − 1 s − 8 \+ 4 1 s − 3 f ( t ) \= 6 ( 1 ) − e 8 t \+ 4 ( e 3 t ) \= 6 − e 8 t \+ 4 e 3 t
b H ( s ) \= 19 s \+ 2 − 1 3 s − 5 \+ 7 s 5 Show Solution
The first term in this case looks like an exponential with a \= − 2 and we’ll need to factor out the 19. Be careful with negative signs in these problems, it’s very easy to lose track of them.
The second term almost looks like an exponential, except that it’s got a 3 s instead of just an s in the denominator. It is an exponential, but in this case, we’ll need to factor a 3 out of the denominator before taking the inverse transform.
The denominator of the third term appears to be [\#3](https://tutorial.math.lamar.edu/classes/de/Laplace_Table.aspx#LT_3) in the table with n \= 4. The numerator however, is not correct for this. There is currently a 7 in the numerator and we need a 4 \! \= 24 in the numerator. This is very easy to fix. Whenever a numerator is off by a multiplicative constant, as in this case, all we need to do is put the constant that we need in the numerator. We will just need to remember to take it back out by dividing by the same constant.
So, let’s first rewrite the transform.
H ( s ) \= 19 s − ( − 2 ) − 1 3 ( s − 5 3 ) \+ 7 4 \! 4 \! s 4 \+ 1 \= 19 1 s − ( − 2 ) − 1 3 1 s − 5 3 \+ 7 4 \! 4 \! s 4 \+ 1
So, what did we do here? We factored the 19 out of the first term. We factored the 3 out of the denominator of the second term since it can’t be there for the inverse transform and in the third term we factored everything out of the numerator except the 4! since that is the portion that we need in the numerator for the inverse transform process.
Let’s now take the inverse transform.
h ( t ) \= 19 e − 2 t − 1 3 e 5 t 3 \+ 7 24 t 4
c F ( s ) \= 6 s s 2 \+ 25 \+ 3 s 2 \+ 25 Show Solution
In this part we’ve got the same denominator in both terms and our table tells us that we’ve either got [\#7](https://tutorial.math.lamar.edu/classes/de/Laplace_Table.aspx#LT_7) or [\#8](https://tutorial.math.lamar.edu/classes/de/Laplace_Table.aspx#LT_8). The numerators will tell us which we’ve actually got. The first one has an s in the numerator and so this means that the first term must be \#8 and we’ll need to factor the 6 out of the numerator in this case. The second term has only a constant in the numerator and so this term must be \#7, however, in order for this to be exactly \#7 we’ll need to multiply/divide a 5 in the numerator to get it correct for the table.
The transform becomes,
F ( s ) \= 6 s s 2 \+ ( 5 ) 2 \+ 3 5 5 s 2 \+ ( 5 ) 2 \= 6 s s 2 \+ ( 5 ) 2 \+ 3 5 5 s 2 \+ ( 5 ) 2
Taking the inverse transform gives,
f ( t ) \= 6 cos ( 5 t ) \+ 3 5 sin ( 5 t )
d G ( s ) \= 8 3 s 2 \+ 12 \+ 3 s 2 − 49 Show Solution
In this case the first term will be a sine once we factor a 3 out of the denominator, while the second term appears to be a hyperbolic sine ([\#17](https://tutorial.math.lamar.edu/classes/de/Laplace_Table.aspx#LT_17)). Again, be careful with the difference between these two. Both of the terms will also need to have their numerators fixed up. Here is the transform once we’re done rewriting it.
G ( s ) \= 1 3 8 s 2 \+ 4 \+ 3 s 2 − 49 \= 1 3 ( 4 ) ( 2 ) s 2 \+ ( 2 ) 2 \+ 3 7 7 s 2 − ( 7 ) 2
Notice that in the first term we took advantage of the fact that we could get the 2 in the numerator that we needed by factoring the 8. The inverse transform is then,
g ( t ) \= 4 3 sin ( 2 t ) \+ 3 7 sinh ( 7 t )
So, probably the best way to identify the transform is by looking at the denominator. If there is more than one possibility use the numerator to identify the correct one. Fix up the numerator if needed to get it into the form needed for the inverse transform process. Finally, take the inverse transform.
Let’s do some slightly harder problems. These are a little more involved than the first set.
Example 2 Find the inverse transform of each of the following.
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Show All Solutions Hide All Solutions
a F ( s ) \= 6 s − 5 s 2 \+ 7 Show Solution
From the denominator of this one it appears that it is either a sine or a cosine. However, the numerator doesn’t match up to either of these in the table. A cosine wants just an s in the numerator with at most a multiplicative constant, while a sine wants only a constant and no s in the numerator.
We’ve got both in the numerator. This is easy to fix however. We will just split up the transform into two terms and then do inverse transforms.
F ( s ) \= 6 s s 2 \+ 7 − 5 7 7 s 2 \+ 7 f ( t ) \= 6 cos ( 7 t ) − 5 7 sin ( 7 t )
Do not get too used to always getting the perfect squares in sines and cosines that we saw in the first set of examples. More often than not (at least in my class) they won’t be perfect squares\!
b F ( s ) \= 1 − 3 s s 2 \+ 8 s \+ 21 Show Solution
In this case there are no denominators in our table that look like this. We can however make the denominator look like one of the denominators in the table by completing the square on the denominator. So, let’s do that first.
s 2 \+ 8 s \+ 21 \= s 2 \+ 8 s \+ 16 − 16 \+ 21 \= s 2 \+ 8 s \+ 16 \+ 5 \= ( s \+ 4 ) 2 \+ 5
Recall that in completing the square you take half the coefficient of the s, square this, and then add and subtract the result to the polynomial. After doing this the first three terms should factor as a perfect square.
So, the transform can be written as the following.
F ( s ) \= 1 − 3 s ( s \+ 4 ) 2 \+ 5
Okay, with this rewrite it looks like we’ve got [\#19](https://tutorial.math.lamar.edu/classes/de/Laplace_Table.aspx#LT_19) and/or [\#20](https://tutorial.math.lamar.edu/classes/de/Laplace_Table.aspx#LT_20)’s from our table of transforms. However, note that in order for it to be a [\#19](https://tutorial.math.lamar.edu/classes/de/Laplace_Table.aspx) we want just a constant in the numerator and in order to be a [\#20](https://tutorial.math.lamar.edu/classes/de/Laplace_Table.aspx) we need an s – a in the numerator. We’ve got neither of these, so we’ll have to correct the numerator to get it into proper form.
In correcting the numerator always get the s – a first. This is the important part. We will also need to be careful of the 3 that sits in front of the s. One way to take care of this is to break the term into two pieces, factor the 3 out of the second and then fix up the numerator of this term. This will work; however, it will put three terms into our answer and there are really only two terms.
So, we will leave the transform as a single term and correct it as follows,
F ( s ) \= 1 − 3 ( s \+ 4 − 4 ) ( s \+ 4 ) 2 \+ 5 \= 1 − 3 ( s \+ 4 ) \+ 12 ( s \+ 4 ) 2 \+ 5 \= − 3 ( s \+ 4 ) \+ 13 ( s \+ 4 ) 2 \+ 5
We needed an s \+ 4 in the numerator, so we put that in. We just needed to make sure and take the 4 back out by subtracting it back out. Also, because of the 3 multiplying the s we needed to do all this inside a set of parenthesis. Then we partially multiplied the 3 through the second term and combined the constants. With the transform in this form, we can break it up into two transforms each of which are in the tables and so we can do inverse transforms on them,
F ( s ) \= − 3 s \+ 4 ( s \+ 4 ) 2 \+ 5 \+ 13 5 5 ( s \+ 4 ) 2 \+ 5 f ( t ) \= − 3 e − 4 t cos ( 5 t ) \+ 13 5 e − 4 t sin ( 5 t )
c G ( s ) \= 3 s − 2 2 s 2 − 6 s − 2 Show Solution
This one is similar to the last one. We just need to be careful with the completing the square however. The first thing that we should do is factor a 2 out of the denominator, then complete the square. Remember that when completing the square a coefficient of 1 on the s 2 term is needed! So, here’s the work for this transform.
G ( s ) \= 3 s − 2 2 ( s 2 − 3 s − 1 ) \= 1 2 3 s − 2 s 2 − 3 s \+ 9 4 − 9 4 − 1 \= 1 2 3 s − 2 ( s − 3 2 ) 2 − 13 4
So, it looks like we’ve got [\#21](https://tutorial.math.lamar.edu/classes/de/Laplace_Table.aspx#LT_21) and [\#22](https://tutorial.math.lamar.edu/classes/de/Laplace_Table.aspx#LT_22) with a corrected numerator. Here’s the work for that and the inverse transform.
G ( s ) \= 1 2 3 ( s − 3 2 \+ 3 2 ) − 2 ( s − 3 2 ) 2 − 13 4 \= 1 2 3 ( s − 3 2 ) \+ 5 2 ( s − 3 2 ) 2 − 13 4 \= 1 2 ( 3 ( s − 3 2 ) ( s − 3 2 ) 2 − 13 4 \+ 5 2 13 13 ( s − 3 2 ) 2 − 13 4 ) g ( t ) \= 1 2 ( 3 e 3 t 2 cosh ( 13 2 t ) \+ 5 13 e 3 t 2 sinh ( 13 2 t ) )
In correcting the numerator of the second term, notice that I only put in the square root since we already had the “over 2” part of the fraction that we needed in the numerator.
d H ( s ) \= s \+ 7 s 2 − 3 s − 10 Show Solution
This one appears to be similar to the previous two, but it actually isn’t. The denominators in the previous two couldn’t be easily factored. In this case the denominator does factor and so we need to deal with it differently. Here is the transform with the factored denominator.
H ( s ) \= s \+ 7 ( s \+ 2 ) ( s − 5 )
The denominator of this transform seems to suggest that we’ve got a couple of exponentials, however in order to be exponentials there can only be a single term in the denominator and no s’s in the numerator.
To fix this we will need to do partial fractions on this transform. In this case the partial fraction decomposition will be
H ( s ) \= A s \+ 2 \+ B s − 5
Don’t remember how to do partial fractions? In this example we’ll show you one way of getting the values of the constants and after this example we’ll review how to get the correct form of the partial fraction decomposition.
Okay, so let’s get the constants. There is a method for finding the constants that will always work, however it can lead to more work than is sometimes required. Eventually, we will need that method, however in this case there is an easier way to find the constants.
Regardless of the method used, the first step is to actually add the two terms back up. This gives the following.
s \+ 7 ( s \+ 2 ) ( s − 5 ) \= A ( s − 5 ) \+ B ( s \+ 2 ) ( s \+ 2 ) ( s − 5 )
Now, this needs to be true for any s that we should choose to put in. So, since the denominators are the same we just need to get the numerators equal. Therefore, set the numerators equal.
s \+ 7 \= A ( s − 5 ) \+ B ( s \+ 2 )
Again, this must be true for ANY value of s that we want to put in. So, let’s take advantage of that. If it must be true for any value of s then it must be true for s \= − 2, to pick a value at random. In this case we get,
5 \= A ( − 7 ) \+ B ( 0 ) ⇒ A \= − 5 7
We found A by appropriately picking s. We can B in the same way if we chose s \= 5.
12 \= A ( 0 ) \+ B ( 7 ) ⇒ B \= 12 7
This will not always work, but when it does it will usually simplify the work considerably.
So, with these constants the transform becomes,
H ( s ) \= − 5 7 s \+ 2 \+ 12 7 s − 5
We can now easily do the inverse transform to get,
h ( t ) \= − 5 7 e − 2 t \+ 12 7 e 5 t
The last part of this example needed partial fractions to get the inverse transform. When we finally get back to differential equations and we start using Laplace transforms to solve them, you will quickly come to understand that partial fractions are a fact of life in these problems. Almost every problem will require partial fractions to one degree or another.
Note that we could have done the last part of this example as we had done the previous two parts. If we had we would have gotten hyperbolic functions. However, recalling the [definition](https://tutorial.math.lamar.edu/classes/de/Laplace_Table.aspx#Note2) of the hyperbolic functions we could have written the result in the form we got from the way we worked our problem. However, most students have a better feel for exponentials than they do for hyperbolic functions and so it’s usually best to just use partial fractions and get the answer in terms of exponentials. It may be a little more work, but it will give a nicer (and easier to work with) form of the answer.
Be warned that in my class I’ve got a rule that if the denominator can be factored with integer coefficients then it must be.
So, let’s remind you how to get the correct partial fraction decomposition. The first step is to factor the denominator as much as possible. Then for each term in the denominator we will use the following table to get a term or terms for our partial fraction decomposition.
| Factor in denominator | Term in partial fraction decomposition |
|---|---|
| a x \+ b | |
Notice that the first and third cases are really special cases of the second and fourth cases respectively.
So, let’s do a couple more examples to remind you how to do partial fractions.
Example 3 Find the inverse transform of each of the following.
1. G
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Show All Solutions Hide All Solutions
a G ( s ) \= 86 s − 78 ( s \+ 3 ) ( s − 4 ) ( 5 s − 1 ) Show Solution
Here’s the partial fraction decomposition for this part.
G ( s ) \= A s \+ 3 \+ B s − 4 \+ C 5 s − 1
Now, this time we won’t go into quite the detail as we did in the last example. We are after the numerator of the partial fraction decomposition and this is usually easy enough to do in our heads. Therefore, we will go straight to setting numerators equal.
86 s − 78 \= A ( s − 4 ) ( 5 s − 1 ) \+ B ( s \+ 3 ) ( 5 s − 1 ) \+ C ( s \+ 3 ) ( s − 4 )
As with the last example, we can easily get the constants by correctly picking values of s.
s \= − 3 − 336 \= A ( − 7 ) ( − 16 ) ⇒ A \= − 3 s \= 1 5 − 304 5 \= C ( 16 5 ) ( − 19 5 ) ⇒ C \= 5 s \= 4 266 \= B ( 7 ) ( 19 ) ⇒ B \= 2
So, the partial fraction decomposition for this transform is,
G ( s ) \= − 3 s \+ 3 \+ 2 s − 4 \+ 5 5 s − 1
Now, in order to actually take the inverse transform we will need to factor a 5 out of the denominator of the last term. The corrected transform as well as its inverse transform is.
G ( s ) \= − 3 s \+ 3 \+ 2 s − 4 \+ 1 s − 1 5 g ( t ) \= − 3 e − 3 t \+ 2 e 4 t \+ e t 5
b F ( s ) \= 2 − 5 s ( s − 6 ) ( s 2 \+ 11 ) Show Solution
So, for the first time we’ve got a quadratic in the denominator. Here’s the decomposition for this part.
F ( s ) \= A s − 6 \+ B s \+ C s 2 \+ 11
Setting numerators equal gives,
2 − 5 s \= A ( s 2 \+ 11 ) \+ ( B s \+ C ) ( s − 6 )
Okay, in this case we could use s \= 6 to quickly find A, but that’s all it would give. In this case we will need to go the “long” way around to getting the constants. Note that this way will always work but is sometimes more work than is required.
The “long” way is to completely multiply out the right side and collect like terms.
2 − 5 s \= A ( s 2 \+ 11 ) \+ ( B s \+ C ) ( s − 6 ) \= A s 2 \+ 11 A \+ B s 2 − 6 B s \+ C s − 6 C \= ( A \+ B ) s 2 \+ ( − 6 B \+ C ) s \+ 11 A − 6 C
In order for these two to be equal the coefficients of the s 2, s and the constants must all be equal. So, setting coefficients equal gives the following system of equations that can be solved.
s 2 : A \+ B \= 0 s 1 : − 6 B \+ C \= − 5 s 0 : 11 A − 6 C \= 2 } ⇒ A \= − 28 47 , B \= 28 47 , C \= − 67 47
Notice that we used s 0 to denote the constants. This is habit on my part and isn’t really required, it’s just what I’m used to doing. Also, the coefficients are fairly messy fractions in this case. Get used to that. They will often be like this when we get back into solving differential equations.
There is a way to make our life a little easier as well with this. Since all of the fractions have a denominator of 47 we’ll factor that out as we plug them back into the decomposition. This will make dealing with them much easier. The partial fraction decomposition is then,
F ( s ) \= 1 47 ( − 28 s − 6 \+ 28 s − 67 s 2 \+ 11 ) \= 1 47 ( − 28 s − 6 \+ 28 s s 2 \+ 11 − 67 11 11 s 2 \+ 11 )
The inverse transform is then.
f ( t ) \= 1 47 ( − 28 e 6 t \+ 28 cos ( 11 t ) − 67 11 sin ( 11 t ) )
c G ( s ) \= 25 s 3 ( s 2 \+ 4 s \+ 5 ) Show Solution
With this last part do not get excited about the s 3. We can think of this term as
s 3 \= ( s − 0 ) 3
and it becomes a linear term to a power. So, the partial fraction decomposition is
G ( s ) \= A s \+ B s 2 \+ C s 3 \+ D s \+ E s 2 \+ 4 s \+ 5
Setting numerators equal and multiplying out gives.
25 \= A s 2 ( s 2 \+ 4 s \+ 5 ) \+ B s ( s 2 \+ 4 s \+ 5 ) \+ C ( s 2 \+ 4 s \+ 5 ) \+ ( D s \+ E ) s 3 \= ( A \+ D ) s 4 \+ ( 4 A \+ B \+ E ) s 3 \+ ( 5 A \+ 4 B \+ C ) s 2 \+ ( 5 B \+ 4 C ) s \+ 5 C
Setting coefficients equal gives the following system.
s 4 : A \+ D \= 0 s 3 : 4 A \+ B \+ E \= 0 s 2 : 5 A \+ 4 B \+ C \= 0 s 1 : 5 B \+ 4 C \= 0 s 0 : 5 C \= 25 } ⇒ A \= 11 5 , B \= − 4 , C \= 5 , D \= − 11 5 , E \= − 24 5
This system looks messy, but it’s easier to solve than it might look. First, we get C for free from the last equation. We can then use the fourth equation to find B. The third equation will then give A, *etc*.
When plugging into the decomposition we’ll get everything with a denominator of 5, then factor that out as we did in the previous part in order to make things easier to deal with.
G ( s ) \= 1 5 ( 11 s − 20 s 2 \+ 25 s 3 − 11 s \+ 24 s 2 \+ 4 s \+ 5 )
Note that we also factored a minus sign out of the last two terms. To complete this part we’ll need to complete the square on the later term and fix up a couple of numerators. Here’s that work.
G ( s ) \= 1 5 ( 11 s − 20 s 2 \+ 25 s 3 − 11 s \+ 24 s 2 \+ 4 s \+ 5 ) \= 1 5 ( 11 s − 20 s 2 \+ 25 s 3 − 11 ( s \+ 2 − 2 ) \+ 24 ( s \+ 2 ) 2 \+ 1 ) \= 1 5 ( 11 s − 20 s 2 \+ 25 2 \! 2 \! s 3 − 11 ( s \+ 2 ) ( s \+ 2 ) 2 \+ 1 − 2 ( s \+ 2 ) 2 \+ 1 )
The inverse transform is then.
g ( t ) \= 1 5 ( 11 − 20 t \+ 25 2 t 2 − 11 e − 2 t cos ( t ) − 2 e − 2 t sin ( t ) )
So, one final time. Partial fractions are a fact of life when using Laplace transforms to solve differential equations. Make sure that you can deal with them. |
| Shard | 16 (laksa) |
| Root Hash | 6561424938415282416 |
| Unparsed URL | edu,lamar!math,tutorial,/classes/de/inversetransforms.aspx s443 |