Calculus: Early Transcendentals 8th Edition

Published by Cengage Learning
ISBN 10: 1285741552
ISBN 13: 978-1-28574-155-0

Chapter 14 - Section 14.3 - Partial Derivatives - 14.3 Exercise - Page 925: 50

Answer

$$ yz+x\ln y=z^{2} $$ To find $\frac{\partial z}{\partial x}$, we differentiate implicitly with respect to $x$, being careful to treat $y$ as a constant: $$ \begin{aligned} \frac{\partial z}{\partial x} &= \frac{\ln y}{(2 z -y )} \\ \end{aligned} $$ To find $\frac{\partial z}{\partial y}$, we differentiate implicitly with respect to $y$, being careful to treat $x$ as a constant: $$ \begin{aligned} \frac{\partial z}{\partial y} &=\frac{x+y z}{y(2 z-y)} \end{aligned} $$

Work Step by Step

$$ yz+x\ln y=z^{2} $$ To find $\frac{\partial z}{\partial x}$, we differentiate implicitly with respect to $x$, being careful to treat $y$ as a constant: $$ \begin{aligned} \frac{\partial }{\partial x} (yz+x\ln y) &=\frac{\partial }{\partial x} (z^{2})\\ y \frac{\partial z}{\partial x}+\ln y &=2 z \frac{\partial z}{\partial x} \\ \ln y &=2 z \frac{\partial z}{\partial x}-y \frac{\partial z}{\partial x} \\ \ln y &=(2 z -y )\frac{\partial z}{\partial x} \\ \\ \frac{\partial z}{\partial x} &= \frac{\ln y}{(2 z -y )} \\ \end{aligned} $$ To find $\frac{\partial z}{\partial y}$, we differentiate implicitly with respect to $y$, being careful to treat $x$ as a constant: $$ \begin{aligned} \frac{\partial }{\partial y} (yz+x\ln y) &=\frac{\partial }{\partial y} (z^{2}) \\ y \frac{\partial z}{\partial y}+z.1+x\frac{1}{y} &=2 z \frac{\partial z}{\partial x} \\ z+\frac{x}{y} &=2 z \frac{\partial z}{\partial x} -y \frac{\partial z}{\partial y} \\ z+\frac{x}{y} &=(2 z -y) \frac{\partial z}{\partial y}\\ \frac{\partial z}{\partial y} &=\frac{z+(x / y)}{2 z-y} \\ &=\frac{x+y z}{y(2 z-y)} \end{aligned} $$
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