Calculus, 10th Edition (Anton)

Published by Wiley
ISBN 10: 0-47064-772-8
ISBN 13: 978-0-47064-772-1

Chapter 13 - Partial Derivatives - 13.3 Partial Derivatives - Exercises Set 13.3 - Page 938: 74

Answer

\[ \begin{aligned} \frac{2 x^{2}+y-z^{3}+3 z^{2}+3 w}{3}=\frac{\partial w}{\partial z} & \end{aligned} \] \[ \begin{aligned} -\frac{1}{3}=\frac{\partial w}{\partial y} & \end{aligned} \] \[ \begin{aligned} -\frac{4 x}{3}=\frac{\partial w}{\partial x} & \end{aligned} \]

Work Step by Step

We are given that \[ z=\ln \left(3 w+ 2 x^{2}+y-z^{3}\right) \] Thus, w is a function of three variables, so differentiating it with respect to $x$ and taking y and z as constant: \[ \begin{aligned} \left(\ln \left(3 w+2 x^{2}+y-z^{3}\right)\right) \frac{\partial}{\partial x}&=\frac{\partial}{\partial x}(z) \\ 0=\frac{1}{2 x^{2}+y-z^{3}+3 w} *\left(4 x+3 \frac{\partial w}{\partial x}\right) & \\ 0=4 x+3 \frac{\partial w}{\partial x} & \\ &-\frac{4 x}{3}=\frac{\partial w}{\partial x} \end{aligned} \] Differentiating it with respect to y: \[ \begin{aligned} \frac{\partial}{\partial y}(z) =\frac{\partial}{\partial y}\left(\ln \left(3 w+2 x^{2}+y-z^{3}\right)\right) &\\ 0=\frac{1}{3 w+2 x^{2}+y-z^{3}} *\left(1+3 \frac{\partial w}{\partial y}\right) & \\ 041+3 \frac{\partial w}{\partial y} & \\ -\frac{1}{3}=\frac{\partial w}{\partial y} & \end{aligned} \] Differentiating it with respect to z: \[ \begin{aligned} \frac{\partial}{\partial z}(z)=\frac{\partial}{\partial z}\left(\ln \left(3 w+2 x^{2}+y-z^{3}\right)\right) & \\ 1=\frac{1}{2 x^{2}+y-z^{3}+3 w} *\left(-3 z^{2}+3 \frac{\partial w}{\partial z}\right) & \\ -3 z^{2}+3 \frac{\partial w}{\partial z} &=3 w+2 x^{2}+y-z^{3} \\ \frac{2 x^{2}+y-z^{3}+3 z^{2}+3 w}{3}=\frac{\partial w}{\partial z} & \end{aligned} \]
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