University Calculus: Early Transcendentals (3rd Edition)

Published by Pearson
ISBN 10: 0321999584
ISBN 13: 978-0-32199-958-0

Chapter 3 - Practice Exercises - Page 205: 142

Answer

$\frac{dZ}{dt}=\frac{-1}{\sqrt{5}}$

Work Step by Step

We are given: $R=10$ and $X=20$ $\frac{dR}{dt}=3$ and $\frac{dX}{dt}=2$ $Z=\sqrt{R^2+X^2}$ diffrentiating above with respect to t: $\frac{dZ}{dt}=\frac{1}{2\sqrt{(R^2+X^2)}}(2R\frac{dR}{dt}+2X\frac{dX}{dt})$ $\frac{dZ}{dt}=\frac{1}{\sqrt{(R^2+X^2)}}(R\frac{dR}{dt}+X\frac{dX}{dt})$ $\frac{dZ}{dt}=\frac{1}{\sqrt{(10^2+20^2)}}(10\times3+20\times-2)$ $\frac{dZ}{dt}=\frac{1}{10\sqrt{(5)}}(-10)$ $\frac{dZ}{dt}=\frac{-1}{\sqrt{5}}$ thus: $\frac{dZ}{dt}=\frac{-1}{\sqrt{5}}$
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