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: 47

Answer

$$ x^{2}+2y^{2}+3z^{2}=1 $$ To find $\frac{\partial z}{\partial x}$, we differentiate implicitly with respect to x, being careful to treat $y$ as a constant: $$ \begin{aligned} \frac{\partial z }{\partial x}&= \frac{-x}{3z }. \end{aligned} $$ To find $\frac{\partial z}{\partial y}$, we differentiate implicitly with respect to x, being careful to treat $x$ as a constant: $$ \begin{aligned} \frac{\partial z }{\partial y}&= \frac{-2y}{3z }. \end{aligned} $$

Work Step by Step

$$ x^{2}+2y^{2}+3z^{2}=1 $$ To find $\frac{\partial z}{\partial x}$, we differentiate implicitly with respect to x, being careful to treat $y$ as a constant: $$ \begin{aligned} \frac{\partial }{\partial x} (x^{2}+2y^{2}+3z^{2}) &=\frac{\partial }{\partial x} (1)\\ \frac{\partial }{\partial x} (x^{2})+2\frac{\partial }{\partial x} ( y^{2}) +3 \frac{\partial }{\partial x} (z^{2} )&=\frac{\partial }{\partial x} (1) \\ 2x +2(0)+3(2z \frac{\partial z }{\partial x}))&=(0) \\ 2x +6z \frac{\partial z }{\partial x}&=0 \\ 6z \frac{\partial z }{\partial x}&=-2x \\ \frac{\partial z }{\partial x}&= \frac{-2x}{6z }= \frac{-x}{3z }. \end{aligned} $$ And to find $\frac{\partial z}{\partial y}$, we differentiate implicitly with respect to x, being careful to treat $x$ as a constant: $$ \begin{aligned} \frac{\partial }{\partial y} (x^{2}+2y^{2}+3z^{2}) &=\frac{\partial }{\partial y} (1)\\ \frac{\partial }{\partial y} (x^{2})+2\frac{\partial }{\partial y} ( y^{2}) +3 \frac{\partial }{\partial y} (z^{2} )&=\frac{\partial }{\partial y} (1) \\ (0) +2(2y)+3(2z \frac{\partial z }{\partial y}))&=(0) \\ 4y +6z \frac{\partial z }{\partial y}&=0 \\ 6z \frac{\partial z }{\partial y}&=-4y \\ \frac{\partial z }{\partial y}&= \frac{-4y}{6z }= \frac{-2y}{3z }. \end{aligned} $$
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