Calculus 8th Edition

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

Chapter 6 - Inverse Functions - 6.4 Derivatives of Logarithmic Functions - 6.4 Exercises - Page 438: 90

Answer

$h'(e)=\frac{1}{e+1}$

Work Step by Step

$h'(x)=(f^{-1})'(x)=\frac{1}{f'(f^{-1}(x))}$ $h'(e)=\frac{1}{f'(f^{-1}(e))}$ So if $f^{-1}(e)=a$ then $e=f(a)$. $e=f(a) \to e=e^{a}+\ln a$ The above equation has a trivial solution at $a=1$ because $e=e^{1}+\ln 1 \to e=e+0 \to e=e$ So $f^{-1}(e)=a \to f^{-1}(e)=1$ $h'(e)=\frac{1}{f'(f^{-1}(e))}\to h'(e)=\frac{1}{f'(1)}$ So the derivative of $f$ is: $f'(x)=(e^{x})'+(\ln x)' \to f'(x)=e^{x}+\frac{1}{x} \to f'(1)=e+\frac{1}{1}=e+1$ $h'(e)=\frac{1}{f'(1)} \to h'(e)=\frac{1}{e+1}$
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