Calculus 8th Edition

Published by Cengage
ISBN 10: 1285740629
ISBN 13: 978-1-28574-062-1

Chapter 14 - Partial Derivatives - 14.3 Partial Derivatives - 14.3 Exercises: 32

Answer

$$\frac{\partial}{\partial x}f(x,y,z)=y^2(1-xz)e^{-xz};$$ $$\frac{\partial}{\partial y}f(x,y,z)=2xye^{-xz};$$ $$\frac{\partial}{\partial z}f(x,y,z)=-x^2y^2e^{-xz}.$$

Work Step by Step

Regard $y$ and $z$ as constant and differentiate with respect to $x$: $$\frac{\partial}{\partial x}f(x,y,z)=\frac{\partial}{\partial x}(xy^2e^{-xz})=y^2\frac{\partial}{\partial x}(xe^{-xz})=y^2\big((x)'_xe^{-xz}+x(e^{-xz})'_x\big)=y^2(e^{-xz}+xe^{-xz}(-xz)'_x)=y^2(e^{-xz}+-xze^{-xz})=y^2(1-xz)e^{-xz}.$$ Regard $x$ and $z$ as constant and differentiate with respect to $y$: $$\frac{\partial}{\partial y}f(x,y,z)=\frac{\partial}{\partial y}(xy^2e^{-xz})=xe^{-xz}\frac{\partial}{\partial y}y^2=2xye^{-xz}.$$ Regard $x$ and $y$ as constant and differentiate with respect to $z$: $$\frac{\partial}{\partial z}f(x,y,z)=\frac{\partial}{\partial z}(xy^2e^{-xz})=xy^2\frac{\partial}{\partial z}e^{-xz}=xy^2e^{-xz}\frac{\partial}{\partial z}(-xz)=xy^2e^{-xz}(-x)=-x^2y^2e^{-xz}.$$
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