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URLhttps://www.cuemath.com/calculus/partial-derivative/
Last Crawled2026-04-13 13:22:03 (1 day ago)
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Meta TitlePartial Derivative (Partial Differentiation) - Calculate, Symbol
Meta DescriptionThe partial derivative of a function with respect to x is the derivative the function treating all other variables than x as constants. Learn how to calculate the partial derivative along with examples and formulas.
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The partial derivative of a function (in two or more variables) is its derivative with respect to one of the variables keeping all the other variables as constants. The process of calculating partial derivative is as same as that of an ordinary derivative except we consider the other variables than the variable with respect to which we are differentiating as constants. Let us learn more about how to calculate partial derivatives of different orders along with examples. 1. What is Partial Derivative? 2. Partial Derivative Symbol 3. How to Calculate Partial Derivatives? 4. Partial Derivatives of Different Orders 5. Partial Differentiation Formulas 6. FAQs on Partial Derivative The partial derivative of a multivariable function, say z = f(x, y), is its derivative with respect to one of the variables, x or y in this case, where the other variables are treated as constants. For example, for finding the partial derivative of f(x, y) with respect to x (which is represented by βˆ‚f / βˆ‚x), y is treated as constant and for finding the partial derivative of f(x, y) with respect to y (which is represented by βˆ‚f / βˆ‚y), x is treated as constant Note that we are not considering all the variables as variables while doing partial differentiation (instead, we are considering only one variable as a variable at a time) and hence the name "partial". The limit definition of a partial derivative looks very similar to the limit definition of the derivative. We can find the partial derivatives using the following limit formulas: βˆ‚f / βˆ‚x = lim h β†’ 0 [ f(x + h, y) - f(x, y) ] / h βˆ‚f / βˆ‚y = lim h β†’ 0 [ f(x, y + h) - f(x, y) ] / h These formulas resemble the derivative definition using the first principle. Example of Partial Derivative If f (x, y) = xy, then find the partial derivative βˆ‚f / βˆ‚x. Solution: βˆ‚f / βˆ‚x = lim h β†’ 0 [ f(x + h, y) - f(x, y) ] / h = lim h β†’ 0 [ (x + h)y - xy ] / h = lim h β†’ 0 [xy + hy - xy] / h = lim h β†’ 0 [hy]/h = lim h β†’ 0 y = y Therefore, βˆ‚f / βˆ‚x = y. We know that the ordinary derivative of a function y = f(x) is denoted by one of the notations dy/dx, d/dx (y), d/dx (f(x)), f '(x), etc. For representing a partial derivative we use the symbol "βˆ‚" instead of "d". We pronounce "βˆ‚" to be "doh" but it has some other names like "partial", "del", "partial dee", "dee", "Jacobi's delta", etc. If z = f(x, y) is a function in two variables then βˆ‚f / βˆ‚x is the partial derivative of f with respect to x βˆ‚f / βˆ‚y is the partial derivative of f with respect to y Just like how we have different symbols of ordinary derivatives, we have different notations for partial derivatives as well. For example, βˆ‚f / βˆ‚x can be written as f x , f x ', D x f, βˆ‚ / βˆ‚x (f), βˆ‚ x f, βˆ‚ / βˆ‚x [f(x, y)], βˆ‚z / βˆ‚x, etc. We have already seen that the limit definitions are used to find the partial derivatives. But using the limit formula and computing the limit is not always easy. Thus, we have another method to calculate partial derivatives that follow right from its definition. In this method, if z = f(x, y) is the function, then we can compute the partial derivatives using the following steps: Step 1 : Identify the variable with respect to which we have to find the partial derivative. Step 2: Except for the variable found in Step 1 , treat all the other variables as constants. Step 3: Differentiate the function just using the rules of ordinary differentiation. Wait! Read Step 3 again. Yes, the rules of ordinary differentiation are as same as that of partial differentiation. In partial differentiation, just treating variables is different, that's it! Example: Let us solve the same above example (If f (x, y) = xy, then find the partial derivative βˆ‚f / βˆ‚x) using the above steps. Solution: We have to find βˆ‚f / βˆ‚x. It means, we have to find the partial derivative of f with respect to x. So we treat y as constant. Thus, we can write 'y' outside the derivative (as in ordinary differentiation, we have a rule that says d/dx (c y) = c dy/dx, where 'c' is a constant). Thus, βˆ‚f / βˆ‚x = βˆ‚ / βˆ‚x (xy) = y βˆ‚ / βˆ‚x (x) = y (1) (Using power rule , d/dx (x) = 1) = y We have got the same answer as we got using the limit definition. We have derivatives like first-order derivatives (like dy/dx), second-order derivatives (like d 2 y/dx 2 ), etc in ordinary derivatives. Likewise, we have first-order, second-order, and higher-order derivatives in partial derivatives also. First Order Partial Derivatives If z = f(x, y) is a function in two variables, then it can have two first-order partial derivatives, namely βˆ‚f / βˆ‚x and βˆ‚f / βˆ‚y. Example: If z = x 2 + y 2 , find all the first order partial derivatives. Solution: f x = βˆ‚f / βˆ‚x = βˆ‚ / βˆ‚x (x 2 + y 2 ) = βˆ‚ / βˆ‚x (x 2 ) + βˆ‚ / βˆ‚x (y 2 ) = 2x + 0 (as y is a constant) = 2x f y = βˆ‚f / βˆ‚y = βˆ‚ / βˆ‚y (x 2 + y 2 ) = βˆ‚ / βˆ‚y (x 2 ) + βˆ‚ / βˆ‚y (y 2 ) = 0 + 2y (as x is a constant) = 2y Second Order Partial Derivatives The second-order partial derivative is obtained by differentiating the function with respect to the indicated variables successively one after the other. If z = f(x, y) is a function in two variables, then it can have four second-order partial derivatives, namely βˆ‚ 2 f / βˆ‚x 2 , βˆ‚ 2 f / βˆ‚y 2 , βˆ‚ 2 f / βˆ‚x βˆ‚y and βˆ‚ 2 f / βˆ‚y βˆ‚β€‹x​​​. To find them, we can first differentiate the function partially with the latter variable, and then partially differentiate the result with respect to the former variable. i.e., f xx = βˆ‚ 2 f / βˆ‚x 2 = βˆ‚ / βˆ‚x (βˆ‚f / βˆ‚x) = βˆ‚ / βˆ‚x (f x ) f yy = βˆ‚ 2 f / βˆ‚y 2 = βˆ‚ / βˆ‚y (βˆ‚f / βˆ‚y) = βˆ‚ / βˆ‚x (f y ) f yx = βˆ‚ 2 f / βˆ‚x βˆ‚y = βˆ‚ / βˆ‚x (βˆ‚f / βˆ‚y) = βˆ‚ / βˆ‚x (f y ) f xy = βˆ‚ 2 f / βˆ‚y βˆ‚x = βˆ‚ / βˆ‚y (βˆ‚f / βˆ‚x) = βˆ‚ / βˆ‚y (f x ) Observe the notations f yx and f xy . The order of variables in each subscript indicate the order of partial differentiation. For example, f yx means to partially differentiate with respect to y first and then with respect to x, and this is same as βˆ‚ 2 f / βˆ‚x βˆ‚y. Example: If z = x 2 + y 2 , find all the second order partial derivatives. Solution: In the above example, we have already found that f x = 2x and f y = 2y. Now, f xx = βˆ‚ / βˆ‚x (f x ) = βˆ‚ / βˆ‚x (2x) = 2 f yy = βˆ‚ / βˆ‚y (f y ) = βˆ‚ / βˆ‚y (2y) = 2 f yx = βˆ‚ / βˆ‚x (f y ) = βˆ‚ / βˆ‚x (2y) = 0 f xy = βˆ‚ / βˆ‚y (f x ) = βˆ‚ / βˆ‚y (2x) = 0 Now that f yx = f xy . Thus, the order of partial differentiation doesn't matter. The process of finding partial derivatives is known as Partial Differentiation. To find the first-order partial derivatives (as discussed earlier) of a function z = f(x, y) we use the following limit formulas: βˆ‚f / βˆ‚x = lim h β†’ 0 [ f(x + h, y) - f(x, y) ] / h βˆ‚f / βˆ‚y = lim h β†’ 0 [ f(x, y + h) - f(x, y) ] / h But instead of using these formulas, just treating all the other variables than the variable with respect to which we are partially differentiating as constants would make the process of partial differentiation very easier. In this process, we just use the same rules as ordinary differentiation and among them, the important rules are as follows: Power Rule The power rule of differentiation says d/dx (x n ) = n x n-1 . The same rule can be applied in partial derivatives also. Example: βˆ‚ / βˆ‚x (x 2 y) = y βˆ‚ / βˆ‚x (x 2 ) = y (2x) = 2xy. Product Rule The product rule of ordinary differentiation says d/dx (uv) = u dv/dx + v du/dx. We can apply the same rule in partial differentiation as well when there are two functions of the same variable. Example: βˆ‚ / βˆ‚x (xy sin x) = y βˆ‚ / βˆ‚x (x sin x) = y [ x βˆ‚ / βˆ‚x (sin x) + sin x βˆ‚ / βˆ‚x (x) ] = y [ x cos x + sin x] Quotient Rule The quotient rule of ordinary differentiation says d/dx (u/v) = [ v du/dx - u dv/dx ] / v 2 . As other rules, this rule can be applied for finding partial derivatives also. Example: βˆ‚ / βˆ‚x ( xy / sin x) = y βˆ‚ / βˆ‚x (x / sin x) = y [ ( sin x βˆ‚ / βˆ‚x (x) - x βˆ‚ / βˆ‚x (sin x) ) / sin 2 x ] = y [ sin x - x cos x] / sin 2 x Chain Rule of Partial Differentiation The chain rule is used when we have to differentiate an implicit function . The chain rule of partial derivatives works a little differently when compared to ordinary derivatives. Sometimes, the rule involves both partial derivatives and ordinary derivatives. There are various forms of this rule and the application of one of them depends upon how each variable of the function is defined. If y = f(x) is a function where x is again a function of two variables u and v (i.e., x = x (u, v)) then βˆ‚f/βˆ‚u = βˆ‚f/βˆ‚x Β· βˆ‚x/βˆ‚u; βˆ‚f/βˆ‚v = βˆ‚f/βˆ‚x Β· βˆ‚x/βˆ‚v If z = f(x, y), where each of x and y are again functions of a variable t (i.e., x = x(t) and y = y(t)) then df/dt = (βˆ‚f/βˆ‚x Β· dx/dt) + (βˆ‚f/βˆ‚y Β· dy/dt) If z = f(x, y) is a function and each of x and y are again functions of two variables u and v (i.e., x = x(u, v) and y = y(u, v)) then βˆ‚f/βˆ‚u = βˆ‚f/βˆ‚x Β· βˆ‚x/βˆ‚u + βˆ‚f/βˆ‚y Β· βˆ‚y/βˆ‚u; βˆ‚f/βˆ‚v = βˆ‚f/βˆ‚x Β· βˆ‚x/βˆ‚v + βˆ‚f/βˆ‚y Β· βˆ‚y/βˆ‚v Example: If z = e xy , where x = uv and y = u + v then find the partial derivative βˆ‚f/βˆ‚u. Solution: By the chain rule of partial derivatives: βˆ‚f/βˆ‚u = βˆ‚f/βˆ‚x Β· βˆ‚x/βˆ‚u + βˆ‚f/βˆ‚y Β· βˆ‚y/βˆ‚u = βˆ‚ / βˆ‚x (e xy ) Β· βˆ‚ / βˆ‚u (uv) + βˆ‚ / βˆ‚y (e xy ) Β· βˆ‚ / βˆ‚u (u + v) = (e xy Β· y) (v) + (e xy Β· x) (1) = e xy (x + vy) Other Rules of Partial Differentiation If f(x, y) = a constant, then the following formula gives the relation between the ordinary derivative and the partial derivatives which follows from implicit differentiation . dy/dx = -f x /f y . For any two functions u(x, y) and v(x, y), the determinant | βˆ‚ u / βˆ‚ x βˆ‚ u / βˆ‚ y βˆ‚ v / βˆ‚ x βˆ‚ v / βˆ‚ y | is known as Jacobian of u and v. The Laplace equation of partial derivatives is βˆ‚ 2 f / βˆ‚x 2 + βˆ‚ 2 f / βˆ‚y 2 + βˆ‚ 2 f / βˆ‚z 2 = 0 where f(x, y, z) is a function in three variables. Any function f that satisfies the Laplace equation is known as the harmonic function. Important Notes on Partial Derivatives: While finding the partial derivative with respect to a variable, all the other variables should be considered as constants. The order of taking derivatives doesn't matter in partial derivatives. i.e., βˆ‚ 2 f / βˆ‚x βˆ‚y = βˆ‚ 2 f / βˆ‚y βˆ‚x. The rules of derivatives apply for partial differentiation as well. Instead of using the limit definition, applying derivative formulas make the process of finding the partial derivatives easier. β˜› Related Topics: Partial Differential Equations Partial Derivative Calculator Read More
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![Download the Cuemath App](https://static.qumath.in/static/next/_next/static/images/app_banner_desktop-8753ba6fb9ffbf8a558f26e1450c864e.webp) ![Download the Cuemath App](https://static.qumath.in/static/next/_next/static/images/app_banner_mobile-3f26e4236459d2a093f12eabcd31dc32.webp) ![Download the Cuemath App](https://static.qumath.in/static/next/_next/static/images/app_banner_desktop-8753ba6fb9ffbf8a558f26e1450c864e.webp) ![Download the Cuemath App](https://static.qumath.in/static/next/_next/static/images/app_banner_mobile-3f26e4236459d2a093f12eabcd31dc32.webp) [Learn]() [Practice]()[Download]() # Partial Derivative The partial derivative of a function (in two or more variables) is its derivative with respect to one of the variables keeping all the other variables as constants. The process of calculating partial derivative is as same as that of an ordinary derivative except we consider the other variables than the variable with respect to which we are differentiating as constants. Let us learn more about how to calculate partial derivatives of different orders along with examples. | | | |---|---| | 1\. | [What is Partial Derivative?](https://www.cuemath.com/calculus/partial-derivative/#a) | | 2\. | [Partial Derivative Symbol](https://www.cuemath.com/calculus/partial-derivative/#b) | | 3\. | [How to Calculate Partial Derivatives?](https://www.cuemath.com/calculus/partial-derivative/#c) | | 4\. | [Partial Derivatives of Different Orders](https://www.cuemath.com/calculus/partial-derivative/#d) | | 5\. | [Partial Differentiation Formulas](https://www.cuemath.com/calculus/partial-derivative/#e) | | 6\. | [FAQs on Partial Derivative](https://www.cuemath.com/calculus/partial-derivative/#faqs) | ## What is Partial Derivative? The **partial derivative** of a multivariable function, say z = f(x, y), is its [derivative](https://www.cuemath.com/calculus/differentiable/) with respect to one of the variables, x or y in this case, where the other variables are treated as constants. For example, - for finding the partial derivative of f(x, y) with respect to x (which is represented by βˆ‚f / βˆ‚x), y is treated as constant and - for finding the partial derivative of f(x, y) with respect to y (which is represented by βˆ‚f / βˆ‚y), x is treated as constant Note that we are not considering all the variables as variables while doing partial differentiation (instead, we are considering only one variable as a variable at a time) and hence the name "partial". The limit definition of a partial derivative looks very similar to the [limit](https://www.cuemath.com/calculus/limits/) definition of the derivative. We can find the partial derivatives using the following limit formulas: - βˆ‚f / βˆ‚x = lim h β†’ 0 \[ f(x + h, y) - f(x, y) \] / h - βˆ‚f / βˆ‚y = lim h β†’ 0 \[ f(x, y + h) - f(x, y) \] / h ![partial derivative formula](https://d138zd1ktt9iqe.cloudfront.net/media/seo_landing_files/partial-derivative-formula-1648621191.png) These formulas resemble the derivative definition using the first principle. ### Example of Partial Derivative If f (x, y) = xy, then find the partial derivative βˆ‚f / βˆ‚x. **Solution:** βˆ‚f / βˆ‚x = lim h β†’ 0 \[ f(x + h, y) - f(x, y) \] / h = lim h β†’ 0 \[ (x + h)y - xy \] / h = lim h β†’ 0 \[xy + hy - xy\] / h = lim h β†’ 0 \[hy\]/h = lim h β†’ 0 y = y Therefore, βˆ‚f / βˆ‚x = y. ## Partial Derivative Symbol We know that the ordinary derivative of a function y = f(x) is denoted by one of the notations dy/dx, d/dx (y), d/dx (f(x)), f '(x), etc. For representing a partial derivative we use the symbol "βˆ‚" instead of "d". We pronounce "βˆ‚" to be "doh" but it has some other names like "partial", "del", "partial dee", "dee", "Jacobi's delta", etc. If z = f(x, y) is a function in two variables then - βˆ‚f / βˆ‚x is the partial derivative of f with respect to x - βˆ‚f / βˆ‚y is the partial derivative of f with respect to y Just like how we have different [symbols](https://www.cuemath.com/numbers/math-symbols/) of ordinary derivatives, we have different notations for partial derivatives as well. For example, βˆ‚f / βˆ‚x can be written as fx, fx', Dxf, βˆ‚ / βˆ‚x (f), βˆ‚x f, βˆ‚ / βˆ‚x \[f(x, y)\], βˆ‚z / βˆ‚x, etc. ## Calculate Partial Derivatives We have already seen that the limit definitions are used to find the partial derivatives. But using the [limit formula](https://www.cuemath.com/limit-formula/) and computing the limit is not always easy. Thus, we have another method to calculate partial derivatives that follow right from its definition. In this method, if z = f(x, y) is the function, then we can compute the partial derivatives using the following steps: - **Step 1**: Identify the variable with respect to which we have to find the partial derivative. - **Step 2:** Except for the variable found in **Step 1**, treat all the other variables as constants. - **Step 3:** Differentiate the function just using the rules of ordinary differentiation. Wait! Read **Step 3** again. Yes, the rules of ordinary differentiation are as same as that of partial differentiation. In partial differentiation, just treating variables is different, that's it\! **Example:** Let us solve the same above example (If f (x, y) = xy, then find the partial derivative βˆ‚f / βˆ‚x) using the above steps. **Solution:** We have to find βˆ‚f / βˆ‚x. It means, we have to find the partial derivative of f with respect to x. So we treat y as constant. Thus, we can write 'y' outside the derivative (as in ordinary differentiation, we have a rule that says d/dx (c y) = c dy/dx, where 'c' is a constant). Thus, βˆ‚f / βˆ‚x = βˆ‚ / βˆ‚x (xy) = y βˆ‚ / βˆ‚x (x) = y (1) (Using [power rule](https://www.cuemath.com/calculus/power-rule/), d/dx (x) = 1) = y We have got the same answer as we got using the limit definition. ## Partial Derivatives of Different Orders We have derivatives like first-order derivatives (like dy/dx), [second-order derivatives](https://www.cuemath.com/calculators/second-derivative-calculator/) (like d2y/dx2), etc in ordinary derivatives. Likewise, we have first-order, second-order, and higher-order derivatives in partial derivatives also. ### First Order Partial Derivatives If z = f(x, y) is a function in two variables, then it can have two first-order partial derivatives, namely βˆ‚f / βˆ‚x and βˆ‚f / βˆ‚y. **Example:** If z = x2 + y2, find all the first order partial derivatives. **Solution:** fx = βˆ‚f / βˆ‚x = βˆ‚ / βˆ‚x (x2 + y2) = βˆ‚ / βˆ‚x (x2) + βˆ‚ / βˆ‚x (y2) = 2x + 0 (as y is a constant) = 2x fy = βˆ‚f / βˆ‚y = βˆ‚ / βˆ‚y (x2 + y2) = βˆ‚ / βˆ‚y (x2) + βˆ‚ / βˆ‚y (y2) = 0 + 2y (as x is a constant) = 2y ### Second Order Partial Derivatives The second-order partial derivative is obtained by differentiating the function with respect to the indicated variables successively one after the other. If z = f(x, y) is a function in two variables, then it can have four second-order partial derivatives, namely βˆ‚2f / βˆ‚x2, βˆ‚2f / βˆ‚y2, βˆ‚2f / βˆ‚x βˆ‚y and βˆ‚2f / βˆ‚y βˆ‚β€‹x​​​. To find them, we can first differentiate the function partially with the latter variable, and then partially differentiate the result with respect to the former variable. i.e., - fxx = βˆ‚2f / βˆ‚x2 = βˆ‚ / βˆ‚x (βˆ‚f / βˆ‚x) = βˆ‚ / βˆ‚x (fx) - fyy = βˆ‚2f / βˆ‚y2 = βˆ‚ / βˆ‚y (βˆ‚f / βˆ‚y) = βˆ‚ / βˆ‚x (fy) - fyx = βˆ‚2f / βˆ‚x βˆ‚y = βˆ‚ / βˆ‚x (βˆ‚f / βˆ‚y) = βˆ‚ / βˆ‚x (fy) - fxy = βˆ‚2f / βˆ‚y βˆ‚x = βˆ‚ / βˆ‚y (βˆ‚f / βˆ‚x) = βˆ‚ / βˆ‚y (fx) Observe the notations fyx and fxy. The order of variables in each subscript indicate the order of partial differentiation. For example, fyx means to partially differentiate with respect to y first and then with respect to x, and this is same as βˆ‚2f / βˆ‚x βˆ‚y. **Example:** If z = x2 + y2, find all the second order partial derivatives. **Solution:** In the above example, we have already found that fx = 2x and fy = 2y. Now, fxx = βˆ‚ / βˆ‚x (fx) = βˆ‚ / βˆ‚x (2x) = 2 fyy = βˆ‚ / βˆ‚y (fy) = βˆ‚ / βˆ‚y (2y) = 2 fyx = βˆ‚ / βˆ‚x (fy) = βˆ‚ / βˆ‚x (2y) = 0 fxy = βˆ‚ / βˆ‚y (fx) = βˆ‚ / βˆ‚y (2x) = 0 Now that fyx = fxy. Thus, the order of partial differentiation doesn't matter. ## Partial Differentiation Formulas The process of finding partial derivatives is known as Partial Differentiation. To find the first-order partial derivatives (as discussed earlier) of a function z = f(x, y) we use the following limit formulas: - βˆ‚f / βˆ‚x = lim h β†’ 0 \[ f(x + h, y) - f(x, y) \] / h - βˆ‚f / βˆ‚y = lim h β†’ 0 \[ f(x, y + h) - f(x, y) \] / h But instead of using these formulas, just treating all the other variables than the variable with respect to which we are partially differentiating as constants would make the process of partial differentiation very easier. In this process, we just use the same [rules as ordinary differentiation](https://www.cuemath.com/calculus/derivative-rules/) and among them, the important rules are as follows: ### Power Rule The power rule of differentiation says d/dx (xn) = n xn-1. The same rule can be applied in partial derivatives also. **Example:** βˆ‚ / βˆ‚x (x2y) = y βˆ‚ / βˆ‚x (x2) = y (2x) = 2xy. ### Product Rule The [product rule](https://www.cuemath.com/calculus/product-rule/) of ordinary differentiation says d/dx (uv) = u dv/dx + v du/dx. We can apply the same rule in partial differentiation as well when there are two functions of the same variable. **Example:** βˆ‚ / βˆ‚x (xy sin x) = y βˆ‚ / βˆ‚x (x sin x) = y \[ x βˆ‚ / βˆ‚x (sin x) + sin x βˆ‚ / βˆ‚x (x) \] = y \[ x cos x + sin x\] ### Quotient Rule The [quotient rule](https://www.cuemath.com/calculus/quotient-rule/) of ordinary differentiation says d/dx (u/v) = \[ v du/dx - u dv/dx \] / v2. As other rules, this rule can be applied for finding partial derivatives also. **Example:** βˆ‚ / βˆ‚x ( xy / sin x) = y βˆ‚ / βˆ‚x (x / sin x) = y \[ ( sin x βˆ‚ / βˆ‚x (x) - x βˆ‚ / βˆ‚x (sin x) ) / sin2x \] = y \[ sin x - x cos x\] / sin2x ### Chain Rule of Partial Differentiation The chain rule is used when we have to differentiate an [implicit function](https://www.cuemath.com/algebra/implicit-function/). The chain rule of partial derivatives works a little differently when compared to ordinary derivatives. Sometimes, the rule involves both partial derivatives and ordinary derivatives. There are various forms of this rule and the application of one of them depends upon how each variable of the function is defined. - If y = f(x) is a function where x is again a function of two variables u and v (i.e., x = x (u, v)) then βˆ‚f/βˆ‚u = βˆ‚f/βˆ‚x Β· βˆ‚x/βˆ‚u; βˆ‚f/βˆ‚v = βˆ‚f/βˆ‚x Β· βˆ‚x/βˆ‚v - If z = f(x, y), where each of x and y are again functions of a variable t (i.e., x = x(t) and y = y(t)) then df/dt = (βˆ‚f/βˆ‚x Β· dx/dt) + (βˆ‚f/βˆ‚y Β· dy/dt) - If z = f(x, y) is a function and each of x and y are again functions of two variables u and v (i.e., x = x(u, v) and y = y(u, v)) then βˆ‚f/βˆ‚u = βˆ‚f/βˆ‚x Β· βˆ‚x/βˆ‚u + βˆ‚f/βˆ‚y Β· βˆ‚y/βˆ‚u; βˆ‚f/βˆ‚v = βˆ‚f/βˆ‚x Β· βˆ‚x/βˆ‚v + βˆ‚f/βˆ‚y Β· βˆ‚y/βˆ‚v **Example:** If z = exy, where x = uv and y = u + v then find the partial derivative βˆ‚f/βˆ‚u. **Solution:** By the chain rule of partial derivatives: βˆ‚f/βˆ‚u = βˆ‚f/βˆ‚x Β· βˆ‚x/βˆ‚u + βˆ‚f/βˆ‚y Β· βˆ‚y/βˆ‚u = βˆ‚ / βˆ‚x (exy) Β· βˆ‚ / βˆ‚u (uv) + βˆ‚ / βˆ‚y (exy) Β· βˆ‚ / βˆ‚u (u + v) = (exy Β· y) (v) + (exy Β· x) (1) = exy (x + vy) ### Other Rules of Partial Differentiation - If f(x, y) = a constant, then the following formula gives the relation between the ordinary derivative and the partial derivatives which follows from [implicit differentiation](https://www.cuemath.com/calculus/implicit-differentiation/). dy/dx = -fx/fy. - For any two functions u(x, y) and v(x, y), the [determinant](https://www.cuemath.com/algebra/determinant-of-matrix/) βˆ£βˆ£βˆ£βˆ‚u/βˆ‚xβˆ‚u/βˆ‚yβˆ‚v/βˆ‚xβˆ‚v/βˆ‚y∣∣∣ \| βˆ‚ u / βˆ‚ x βˆ‚ u / βˆ‚ y βˆ‚ v / βˆ‚ x βˆ‚ v / βˆ‚ y \| is known as **Jacobian** of u and v. - The **Laplace equation** of partial derivatives is βˆ‚2f / βˆ‚x2 + βˆ‚2f / βˆ‚y2 + βˆ‚2f / βˆ‚z2 = 0 where f(x, y, z) is a function in three variables. Any function f that satisfies the Laplace equation is known as the harmonic function. **Important Notes on Partial Derivatives:** - While finding the partial derivative with respect to a variable, all the other variables should be considered as constants. - The order of taking derivatives doesn't matter in partial derivatives. i.e., βˆ‚2f / βˆ‚x βˆ‚y = βˆ‚2f / βˆ‚y βˆ‚x. - The rules of derivatives apply for partial differentiation as well. - Instead of using the limit definition, applying [derivative formulas](https://www.cuemath.com/derivative-formula/) make the process of finding the partial derivatives easier. β˜› **Related Topics:** - [Partial Differential Equations](https://www.cuemath.com/calculus/partial-differential-equations/) - [Partial Derivative Calculator](https://www.cuemath.com/calculators/partial-derivative-calculator/) Read More Explore math program Download FREE Study Materials ![](data:image/svg+xml;base64,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) SHEETS ![](https://d138zd1ktt9iqe.cloudfront.net/media/seo_landing_files/thumbnails/partial-derivative-worksheet-newui-first-page-1649086216.jpg) Partial Derivative Worksheet Calculus Worksheet ![](data:image/svg+xml;base64,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) ## Partial Derivative Examples 1. **Example 1:** Find all the first order partial derivatives of the function f(x, y) = ax2 + 2hxy + by2. **Solution:** The first-order partial derivatives are: fx = βˆ‚f / βˆ‚x = βˆ‚ / βˆ‚x (ax2 + 2hxy + by2) = βˆ‚ / βˆ‚x (ax2) + βˆ‚ / βˆ‚x (2hxy) + βˆ‚ / βˆ‚x (by2) = 2ax + 2hy (1) + 0 (as y is a constant) = 2ax + 2hy fx = βˆ‚f / βˆ‚x = βˆ‚ / βˆ‚x (ax2 + 2hxy + by2) = βˆ‚ / βˆ‚y (ax2) + βˆ‚ / βˆ‚y (2hxy) + βˆ‚ / βˆ‚y (by2) = 0 + 2hx (1) + 2by (as x is a constant) = 2hx + 2by **Answer:** fx = 2ax + 2hy and fy = 2hx + 2by. 2. **Example 2:** Find all the second-order partial derivatives of the function given in **Example 1.** **Solution:** We found in **Example 1** thatfx = 2ax + 2hy and fy = 2hx + 2by. Now, we will find the second-order partial derivatives. fxx = βˆ‚ / βˆ‚x (fx) = βˆ‚ / βˆ‚x (2ax + 2hy) = 2a fyy = βˆ‚ / βˆ‚y (fy) = βˆ‚ / βˆ‚y (2hx + 2by) = 2b fyx = βˆ‚ / βˆ‚x (fy) = βˆ‚ / βˆ‚x (2hx + 2by) = 2h fxy = βˆ‚ / βˆ‚y (fx) = βˆ‚ / βˆ‚y (2ax + 2hy) = 2h **Answer:** We found that fxx = 2a, fyy = 2b, fyx = 2h, and fxy = 2h. 3. **Example 3:** Does the order of differentiation matter while finding the partial derivatives? Justify your answer using **Example 2.** **Solution:** From **Example 2**, fyx = 2h and fxy = 2h. Thus, fxy = fxy. Thus, the order of partial differentiation doesn't matter. **Answer:** The order doesn't matter as fyx = fxy. View Answer \> ![](https://d138zd1ktt9iqe.cloudfront.net/media/seo_landing_files/caucasian-kid-and-indian-teacher-grade-4-7-1619081163.png) Great learning in high school using simple cues Indulging in rote learning, you are likely to forget concepts. With Cuemath, you will learn visually and be surprised by the outcomes. [Book a Free Trial Class](https://www.cuemath.com/parent/signup/) ## Practice Questions on Partial Differentiation Check Answer \> ## FAQs on Partial Derivative ### How to Calculate Partial Derivatives? We use **partial derivatives** when the function has more than one variable. If a function f is in terms of two variables x and y, then we can calculate the partial derivatives as follows. - the partial derivative of f = βˆ‚f/βˆ‚x and y has to be treated as constant here. - the partial derivative of f = βˆ‚f/βˆ‚y and x has to be treated as constant here. ### What is the Symbol of Partial Derivatives? We use the symbol βˆ‚ to represent a partial derivative. For example, the partial derivative of a function f(x, y) with respect to x is written as βˆ‚f/βˆ‚x. ### What is the Difference Between Differentiation and Partial Differentiation? We talk about the [derivative](https://www.cuemath.com/calculus/derivatives/) of a function if a function has only one variable in it. For example, the derivative of a function y = f(x) is denoted by df/dx. We talk about partial derivatives when a function z = f(x, y) has more than one variable. The partial derivative of f with respect to x is denoted by βˆ‚f/βˆ‚x and while finding this, we treat y as constant. ### What is the Formula Used to Find the Partial Derivative? The partial derivatives of a function z = f(x, y) can be found using the limit formulas: - βˆ‚f / βˆ‚x = lim h β†’ 0 \[ f(x + h, y) - f(x, y) \] / h - βˆ‚f / βˆ‚y = lim h β†’ 0 \[ f(x, y + h) - f(x, y) \] / h ### What Does Partial Derivative Tell Us? Partial derivative tells us to [differentiate](https://www.cuemath.com/calculus/differentiation/) a function partially. It means if we are differentiating partially with respect to one variable, then the remaining [variables](https://www.cuemath.com/algebra/variables-constants-and-expressions/) of the function must be treated as constants. ### What is the Chain Rule of Partial Derivatives? The chain rule of partial derivative is mentioned below: If z = f(x, y) is a [function](https://www.cuemath.com/calculus/What-are-functions/) where x and y are functions of two variables u and v (i.e., x = x(u, v) and y = y(u, v)) then by the chain rule of partial derivatives, - βˆ‚f/βˆ‚u = βˆ‚f/βˆ‚x Β· βˆ‚x/βˆ‚u + βˆ‚f/βˆ‚y Β· βˆ‚y/βˆ‚u - βˆ‚f/βˆ‚v = βˆ‚f/βˆ‚x Β· βˆ‚x/βˆ‚v + βˆ‚f/βˆ‚y Β· βˆ‚y/βˆ‚v ### What is the Formula that Connects Normal Derivatives with Partial Derivatives? When f(x, y) = c, where 'c' is a [constant](https://www.cuemath.com/algebra/constants/), then dy/dx = -fx/fy, where - fx is the partial derivative of f with respect to x - fy is the partial derivative of f with respect to y Explore math program Math worksheets and visual curriculum Download App Become MathFitβ„’: Boost math skills with daily fun challenges and puzzles. Download the app STRATEGY GAMES LOGIC PUZZLES MENTAL MATH Become MathFitβ„’: Boost math skills with daily fun challenges and puzzles. 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The partial derivative of a function (in two or more variables) is its derivative with respect to one of the variables keeping all the other variables as constants. The process of calculating partial derivative is as same as that of an ordinary derivative except we consider the other variables than the variable with respect to which we are differentiating as constants. Let us learn more about how to calculate partial derivatives of different orders along with examples. | | | |---|---| | 1\. | [What is Partial Derivative?](https://www.cuemath.com/calculus/partial-derivative/#a) | | 2\. | [Partial Derivative Symbol](https://www.cuemath.com/calculus/partial-derivative/#b) | | 3\. | [How to Calculate Partial Derivatives?](https://www.cuemath.com/calculus/partial-derivative/#c) | | 4\. | [Partial Derivatives of Different Orders](https://www.cuemath.com/calculus/partial-derivative/#d) | | 5\. | [Partial Differentiation Formulas](https://www.cuemath.com/calculus/partial-derivative/#e) | | 6\. | [FAQs on Partial Derivative](https://www.cuemath.com/calculus/partial-derivative/#faqs) | The **partial derivative** of a multivariable function, say z = f(x, y), is its [derivative](https://www.cuemath.com/calculus/differentiable/) with respect to one of the variables, x or y in this case, where the other variables are treated as constants. For example, - for finding the partial derivative of f(x, y) with respect to x (which is represented by βˆ‚f / βˆ‚x), y is treated as constant and - for finding the partial derivative of f(x, y) with respect to y (which is represented by βˆ‚f / βˆ‚y), x is treated as constant Note that we are not considering all the variables as variables while doing partial differentiation (instead, we are considering only one variable as a variable at a time) and hence the name "partial". The limit definition of a partial derivative looks very similar to the [limit](https://www.cuemath.com/calculus/limits/) definition of the derivative. We can find the partial derivatives using the following limit formulas: - βˆ‚f / βˆ‚x = lim h β†’ 0 \[ f(x + h, y) - f(x, y) \] / h - βˆ‚f / βˆ‚y = lim h β†’ 0 \[ f(x, y + h) - f(x, y) \] / h These formulas resemble the derivative definition using the first principle. ### Example of Partial Derivative If f (x, y) = xy, then find the partial derivative βˆ‚f / βˆ‚x. **Solution:** βˆ‚f / βˆ‚x = lim h β†’ 0 \[ f(x + h, y) - f(x, y) \] / h = lim h β†’ 0 \[ (x + h)y - xy \] / h = lim h β†’ 0 \[xy + hy - xy\] / h = lim h β†’ 0 \[hy\]/h = lim h β†’ 0 y = y Therefore, βˆ‚f / βˆ‚x = y. We know that the ordinary derivative of a function y = f(x) is denoted by one of the notations dy/dx, d/dx (y), d/dx (f(x)), f '(x), etc. For representing a partial derivative we use the symbol "βˆ‚" instead of "d". We pronounce "βˆ‚" to be "doh" but it has some other names like "partial", "del", "partial dee", "dee", "Jacobi's delta", etc. If z = f(x, y) is a function in two variables then - βˆ‚f / βˆ‚x is the partial derivative of f with respect to x - βˆ‚f / βˆ‚y is the partial derivative of f with respect to y Just like how we have different [symbols](https://www.cuemath.com/numbers/math-symbols/) of ordinary derivatives, we have different notations for partial derivatives as well. For example, βˆ‚f / βˆ‚x can be written as fx, fx', Dxf, βˆ‚ / βˆ‚x (f), βˆ‚x f, βˆ‚ / βˆ‚x \[f(x, y)\], βˆ‚z / βˆ‚x, etc. We have already seen that the limit definitions are used to find the partial derivatives. But using the [limit formula](https://www.cuemath.com/limit-formula/) and computing the limit is not always easy. Thus, we have another method to calculate partial derivatives that follow right from its definition. In this method, if z = f(x, y) is the function, then we can compute the partial derivatives using the following steps: - **Step 1**: Identify the variable with respect to which we have to find the partial derivative. - **Step 2:** Except for the variable found in **Step 1**, treat all the other variables as constants. - **Step 3:** Differentiate the function just using the rules of ordinary differentiation. Wait! Read **Step 3** again. Yes, the rules of ordinary differentiation are as same as that of partial differentiation. In partial differentiation, just treating variables is different, that's it\! **Example:** Let us solve the same above example (If f (x, y) = xy, then find the partial derivative βˆ‚f / βˆ‚x) using the above steps. **Solution:** We have to find βˆ‚f / βˆ‚x. It means, we have to find the partial derivative of f with respect to x. So we treat y as constant. Thus, we can write 'y' outside the derivative (as in ordinary differentiation, we have a rule that says d/dx (c y) = c dy/dx, where 'c' is a constant). Thus, βˆ‚f / βˆ‚x = βˆ‚ / βˆ‚x (xy) = y βˆ‚ / βˆ‚x (x) = y (1) (Using [power rule](https://www.cuemath.com/calculus/power-rule/), d/dx (x) = 1) = y We have got the same answer as we got using the limit definition. We have derivatives like first-order derivatives (like dy/dx), [second-order derivatives](https://www.cuemath.com/calculators/second-derivative-calculator/) (like d2y/dx2), etc in ordinary derivatives. Likewise, we have first-order, second-order, and higher-order derivatives in partial derivatives also. ### First Order Partial Derivatives If z = f(x, y) is a function in two variables, then it can have two first-order partial derivatives, namely βˆ‚f / βˆ‚x and βˆ‚f / βˆ‚y. **Example:** If z = x2 + y2, find all the first order partial derivatives. **Solution:** fx = βˆ‚f / βˆ‚x = βˆ‚ / βˆ‚x (x2 + y2) = βˆ‚ / βˆ‚x (x2) + βˆ‚ / βˆ‚x (y2) = 2x + 0 (as y is a constant) = 2x fy = βˆ‚f / βˆ‚y = βˆ‚ / βˆ‚y (x2 + y2) = βˆ‚ / βˆ‚y (x2) + βˆ‚ / βˆ‚y (y2) = 0 + 2y (as x is a constant) = 2y ### Second Order Partial Derivatives The second-order partial derivative is obtained by differentiating the function with respect to the indicated variables successively one after the other. If z = f(x, y) is a function in two variables, then it can have four second-order partial derivatives, namely βˆ‚2f / βˆ‚x2, βˆ‚2f / βˆ‚y2, βˆ‚2f / βˆ‚x βˆ‚y and βˆ‚2f / βˆ‚y βˆ‚β€‹x​​​. To find them, we can first differentiate the function partially with the latter variable, and then partially differentiate the result with respect to the former variable. i.e., - fxx = βˆ‚2f / βˆ‚x2 = βˆ‚ / βˆ‚x (βˆ‚f / βˆ‚x) = βˆ‚ / βˆ‚x (fx) - fyy = βˆ‚2f / βˆ‚y2 = βˆ‚ / βˆ‚y (βˆ‚f / βˆ‚y) = βˆ‚ / βˆ‚x (fy) - fyx = βˆ‚2f / βˆ‚x βˆ‚y = βˆ‚ / βˆ‚x (βˆ‚f / βˆ‚y) = βˆ‚ / βˆ‚x (fy) - fxy = βˆ‚2f / βˆ‚y βˆ‚x = βˆ‚ / βˆ‚y (βˆ‚f / βˆ‚x) = βˆ‚ / βˆ‚y (fx) Observe the notations fyx and fxy. The order of variables in each subscript indicate the order of partial differentiation. For example, fyx means to partially differentiate with respect to y first and then with respect to x, and this is same as βˆ‚2f / βˆ‚x βˆ‚y. **Example:** If z = x2 + y2, find all the second order partial derivatives. **Solution:** In the above example, we have already found that fx = 2x and fy = 2y. Now, fxx = βˆ‚ / βˆ‚x (fx) = βˆ‚ / βˆ‚x (2x) = 2 fyy = βˆ‚ / βˆ‚y (fy) = βˆ‚ / βˆ‚y (2y) = 2 fyx = βˆ‚ / βˆ‚x (fy) = βˆ‚ / βˆ‚x (2y) = 0 fxy = βˆ‚ / βˆ‚y (fx) = βˆ‚ / βˆ‚y (2x) = 0 Now that fyx = fxy. Thus, the order of partial differentiation doesn't matter. The process of finding partial derivatives is known as Partial Differentiation. To find the first-order partial derivatives (as discussed earlier) of a function z = f(x, y) we use the following limit formulas: - βˆ‚f / βˆ‚x = lim h β†’ 0 \[ f(x + h, y) - f(x, y) \] / h - βˆ‚f / βˆ‚y = lim h β†’ 0 \[ f(x, y + h) - f(x, y) \] / h But instead of using these formulas, just treating all the other variables than the variable with respect to which we are partially differentiating as constants would make the process of partial differentiation very easier. In this process, we just use the same [rules as ordinary differentiation](https://www.cuemath.com/calculus/derivative-rules/) and among them, the important rules are as follows: ### Power Rule The power rule of differentiation says d/dx (xn) = n xn-1. The same rule can be applied in partial derivatives also. **Example:** βˆ‚ / βˆ‚x (x2y) = y βˆ‚ / βˆ‚x (x2) = y (2x) = 2xy. ### Product Rule The [product rule](https://www.cuemath.com/calculus/product-rule/) of ordinary differentiation says d/dx (uv) = u dv/dx + v du/dx. We can apply the same rule in partial differentiation as well when there are two functions of the same variable. **Example:** βˆ‚ / βˆ‚x (xy sin x) = y βˆ‚ / βˆ‚x (x sin x) = y \[ x βˆ‚ / βˆ‚x (sin x) + sin x βˆ‚ / βˆ‚x (x) \] = y \[ x cos x + sin x\] ### Quotient Rule The [quotient rule](https://www.cuemath.com/calculus/quotient-rule/) of ordinary differentiation says d/dx (u/v) = \[ v du/dx - u dv/dx \] / v2. As other rules, this rule can be applied for finding partial derivatives also. **Example:** βˆ‚ / βˆ‚x ( xy / sin x) = y βˆ‚ / βˆ‚x (x / sin x) = y \[ ( sin x βˆ‚ / βˆ‚x (x) - x βˆ‚ / βˆ‚x (sin x) ) / sin2x \] = y \[ sin x - x cos x\] / sin2x ### Chain Rule of Partial Differentiation The chain rule is used when we have to differentiate an [implicit function](https://www.cuemath.com/algebra/implicit-function/). The chain rule of partial derivatives works a little differently when compared to ordinary derivatives. Sometimes, the rule involves both partial derivatives and ordinary derivatives. There are various forms of this rule and the application of one of them depends upon how each variable of the function is defined. - If y = f(x) is a function where x is again a function of two variables u and v (i.e., x = x (u, v)) then βˆ‚f/βˆ‚u = βˆ‚f/βˆ‚x Β· βˆ‚x/βˆ‚u; βˆ‚f/βˆ‚v = βˆ‚f/βˆ‚x Β· βˆ‚x/βˆ‚v - If z = f(x, y), where each of x and y are again functions of a variable t (i.e., x = x(t) and y = y(t)) then df/dt = (βˆ‚f/βˆ‚x Β· dx/dt) + (βˆ‚f/βˆ‚y Β· dy/dt) - If z = f(x, y) is a function and each of x and y are again functions of two variables u and v (i.e., x = x(u, v) and y = y(u, v)) then βˆ‚f/βˆ‚u = βˆ‚f/βˆ‚x Β· βˆ‚x/βˆ‚u + βˆ‚f/βˆ‚y Β· βˆ‚y/βˆ‚u; βˆ‚f/βˆ‚v = βˆ‚f/βˆ‚x Β· βˆ‚x/βˆ‚v + βˆ‚f/βˆ‚y Β· βˆ‚y/βˆ‚v **Example:** If z = exy, where x = uv and y = u + v then find the partial derivative βˆ‚f/βˆ‚u. **Solution:** By the chain rule of partial derivatives: βˆ‚f/βˆ‚u = βˆ‚f/βˆ‚x Β· βˆ‚x/βˆ‚u + βˆ‚f/βˆ‚y Β· βˆ‚y/βˆ‚u = βˆ‚ / βˆ‚x (exy) Β· βˆ‚ / βˆ‚u (uv) + βˆ‚ / βˆ‚y (exy) Β· βˆ‚ / βˆ‚u (u + v) = (exy Β· y) (v) + (exy Β· x) (1) = exy (x + vy) ### Other Rules of Partial Differentiation - If f(x, y) = a constant, then the following formula gives the relation between the ordinary derivative and the partial derivatives which follows from [implicit differentiation](https://www.cuemath.com/calculus/implicit-differentiation/). dy/dx = -fx/fy. - For any two functions u(x, y) and v(x, y), the [determinant](https://www.cuemath.com/algebra/determinant-of-matrix/) \| βˆ‚ u / βˆ‚ x βˆ‚ u / βˆ‚ y βˆ‚ v / βˆ‚ x βˆ‚ v / βˆ‚ y \| is known as **Jacobian** of u and v. - The **Laplace equation** of partial derivatives is βˆ‚2f / βˆ‚x2 + βˆ‚2f / βˆ‚y2 + βˆ‚2f / βˆ‚z2 = 0 where f(x, y, z) is a function in three variables. Any function f that satisfies the Laplace equation is known as the harmonic function. **Important Notes on Partial Derivatives:** - While finding the partial derivative with respect to a variable, all the other variables should be considered as constants. - The order of taking derivatives doesn't matter in partial derivatives. i.e., βˆ‚2f / βˆ‚x βˆ‚y = βˆ‚2f / βˆ‚y βˆ‚x. - The rules of derivatives apply for partial differentiation as well. - Instead of using the limit definition, applying [derivative formulas](https://www.cuemath.com/derivative-formula/) make the process of finding the partial derivatives easier. β˜› **Related Topics:** - [Partial Differential Equations](https://www.cuemath.com/calculus/partial-differential-equations/) - [Partial Derivative Calculator](https://www.cuemath.com/calculators/partial-derivative-calculator/) Read More
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