Calculus: Early Transcendentals (2nd Edition)

Published by Pearson
ISBN 10: 0321947347
ISBN 13: 978-0-32194-734-5

Chapter 9 - Power Series - 9.4 Working with Taylor Series - 9.4 Exercises - Page 703: 52

Answer

$\dfrac{e^2+1}{4}$

Work Step by Step

The first $4$ non-zero terms of Taylor series can be written as: $e^x=1+x+\dfrac{x^2}{2!}+\dfrac{x^3}{3!}+.......$ Now, we have: $\dfrac{e^x-1}{x}=\dfrac{(1+x+\dfrac{x^2}{2!}+\dfrac{x^3}{3!}+.......)-1}{x}=\Sigma_{k=0}^{\infty} \dfrac{x^k}{(k+1)!}$ Next, $f'(x)=\dfrac{e^x(x-1)+1}{x^2}=\Sigma_{k=0}^{\infty} \dfrac{kx^{k-1}}{(k+1)!}$ Plug $x=1$ in the above equation to obtain: $f'(2)=\Sigma_{k=0}^{\infty} \dfrac{k(2^{k-1})}{(k+1)!}=\dfrac{e^2+1}{4}$
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