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: 73

Answer

\[ \begin{aligned} \frac{\partial w}{z} &=-\frac{z}{w} \\ \frac{\partial w}{\partial x} &=-\frac{x}{w} \\ \frac{\partial w}{y} &=-\frac{y}{w} \end{aligned} \]

Work Step by Step

We are given that \[ 4=\left(w^{2}+x^{2}+y^{2}+z^{2}\right)^{3 / 2} \] Thus, w is a function of three variable, so differentiating it with respect to $x$: \[ \begin{aligned} \frac{\partial}{\partial x}\left(\left(x^{2}+y^{2}+z^{2}+w^{2}\right)^{3 / 2}\right) &=\frac{d}{d x}(4) \\ \frac{3}{2} \sqrt{x^{2}+y^{2}+z^{2}+w^{2}} *\left(2 x+2 w \frac{\partial w}{\partial x}\right) &=0 \quad \because \sqrt{x^{2}+y^{2}+z^{2}+w^{2}}=\text { positive number } \\ 2 x+2 w \frac{\partial w}{\partial x} &=0 \\ \frac{\partial w}{\partial x} &=-\frac{x}{w} \end{aligned} \] Differentiating it with respect to y: \[ \begin{aligned} \frac{\partial}{\partial y}\left(\left(x^{2}+y^{2}+z^{2}+w^{2}\right)^{3 / 2}\right) &=\frac{d}{d y}(1) \\ \frac{3}{2} \sqrt{x^{2}+y^{2}+z^{2}+w^{2}} *\left(2 y+2 w \frac{\partial w}{\partial y}\right) &=0 \quad \because \sqrt{x^{2}+y^{2}+z^{2}+w^{2}}=\text { positive number } \\ 2 y+2 w \frac{\partial w}{\partial y} &=0 \\ -\frac{y}{w}=\frac{\partial w}{\partial x} & \end{aligned} \] Differentiating it with respect to z: \[ \begin{aligned} \frac{d}{d z}(1)=\frac{\partial}{\partial z}\left(\left(w^{2}+x^{2}+y^{2}+z^{2}\right)^{3 / 2}\right) & \\ \frac{3}{2} \sqrt{w^{2}+x^{2}+y^{2}+z^{2}} *\left(2 y+2 w \frac{\partial w}{\partial z}\right) &=0 \quad \because \sqrt{w^{2}+x^{2}+y^{2}+z^{2}}=\text { positive number } \\ 0=2 z+2 w \frac{\partial w}{\partial z} & \\ -\frac{z}{w}=\frac{\partial w}{\partial z} & \end{aligned} \]
Update this answer!

You can help us out by revising, improving and updating this answer.

Update this answer

After you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.