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: 69

Answer

\[ -\frac{x}{z}=\frac{\partial z}{\partial x} \] \[ -\frac{y}{z}=\frac{\partial z}{\partial y} \]

Work Step by Step

We are given that \[ 1=\left(z^{2}+y^{2}+x^{2}\right)^{3 / 2} \] Differentiate the variable $ z $ in relation to $ x $ with $ y $ constant \[ \begin{aligned} \frac{\partial}{\partial x}\left(\left(x^{2}+y^{2}+z^{2}\right)^{3 / 2}\right) &=\frac{d}{d x}(1) \\ \frac{3}{2} \sqrt{x^{2}+y^{2}+z^{2}} *\left(2 x+2 z \frac{\partial z}{\partial x}\right) &=0 \quad \because \sqrt{x^{2}+y^{2}+z^{2}}=1 \\ 2 x+2 z \frac{\partial z}{\partial x} &=0 \\ -\frac{x}{z}=\frac{\partial z}{\partial x} & \end{aligned} \] And: \[ \begin{aligned} \frac{d}{d y}(1)=\frac{\partial}{\partial y}\left(\left(z^{2}+y^{2}+x^{2}\right)^{3 / 2}\right) & \\ 0=\frac{3}{2} \sqrt{x^{2}+y^{2}+z^{2}} *\left(2 y+2 z \frac{\partial z}{\partial y}\right) & \quad \because1= \sqrt{z^{2}+y^{2}+x^{2}} \\ 0=2 y+2 z \frac{\partial z}{\partial y} & \\ -\frac{y}{z}=\frac{\partial z}{\partial y} & \end{aligned} \]
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