University Calculus: Early Transcendentals (3rd Edition)

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

Chapter 4 - Section 4.5 - Indeterminate Forms and L'Hôpital's Rule - Exercises - Page 248: 20

Answer

$\dfrac{1}{1 +\pi}$

Work Step by Step

Consider: $\lim\limits_{x \to 1}f(x)=\lim\limits_{x \to 1}\dfrac{x-1}{\ln x-\sin (\pi x)}$ Now, $f(1)=\dfrac{1-1}{\ln 1-\sin (1) \pi}=\dfrac{0}{0}$ The limit shows an indeterminate form. Thus, apply L-Hospital's rule: $\lim\limits_{a \to b}f(x)=\lim\limits_{a \to b}\dfrac{g'(x)}{h'(x)}$ Thus: $\lim\limits_{x \to 1}\dfrac{1}{\dfrac{1}{x}-\pi \cos (\pi x)}=\dfrac{1}{1-\pi \cos (\pi)}=\dfrac{1}{1 +\pi}$
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