Calculus 8th Edition

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

Chapter 2 - Derivatives - 2.5 The Chain Rule - 2.5 Exercises - Page 159: 68

Answer

\[(a)F'(x)=\;\alpha x^{\alpha-1}f'(x^{\alpha})\] \[(b)\;G'(x)=\alpha f'(x)[f(x)]^{\alpha-1}\: \]

Work Step by Step

\[(a) \; F(x)=f(x^{\alpha})\] Differentiate with respect to $x$ using chain rule \[ F'(x)=f'(x^{\alpha})\cdot \;(x^{\alpha})'\] \[ F'(x)=f'(x^{\alpha})\cdot \;(\alpha x^{\alpha-1})\] \[F'(x)=\alpha x^{\alpha-1}f'(x^{\alpha})\] Hence, \[F'(x)=\alpha x^{\alpha-1}f'(x^{\alpha})\] \[(b)\; G(x)=[f(x)]^{\alpha}\] Differentiate with respect to $x$ using chain rule Because $\alpha$ is real number \[G'(x)=\alpha[f(x)]^{\alpha-1}\: \{f(x)\}'\] \[G'(x)=\alpha f'(x)[f(x)]^{\alpha-1}\: \] Hence, \[G'(x)=\alpha f'(x)[f(x)]^{\alpha-1}\: \]
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