Calculus: Early Transcendentals (2nd Edition)

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

Chapter 6 - Applications of Integration - 6.10 Hyperbolic Functions - 6.10 Exercises - Page 505: 86

Answer

$$0$$

Work Step by Step

$$\eqalign{ & \mathop {\lim }\limits_{x \to {1^ - }} \frac{{{{\tanh }^{ - 1}}x}}{{\tan \left( {\pi x/2} \right)}} \cr & {\text{Evaluate the limit by direct substitution}} \cr & \mathop {\lim }\limits_{x \to {1^ - }} \frac{{{{\tanh }^{ - 1}}x}}{{\tan \left( {\pi x/2} \right)}} = \frac{{{{\tanh }^{ - 1}}\left( 1 \right)}}{{\tan \left( {\pi /2} \right)}} \cr & {\text{ }} = \frac{\infty }{\infty } \cr & {\text{Use L'Hopital's Rule}} \cr & \mathop {\lim }\limits_{x \to {1^ - }} \frac{{{{\tanh }^{ - 1}}x}}{{\tan \left( {\pi x/2} \right)}} = \mathop {\lim }\limits_{x \to {1^ - }} \frac{{\frac{d}{{dx}}\left[ {{{\tanh }^{ - 1}}x} \right]}}{{\frac{d}{{dx}}\left[ {\tan \left( {\pi x/2} \right)} \right]}} \cr & {\text{ }} = \mathop {\lim }\limits_{x \to {1^ - }} \frac{{\frac{1}{{1 - {x^2}}}}}{{{{\sec }^2}\left( {\frac{{\pi x}}{2}} \right)\left( {\frac{\pi }{2}} \right)}} \cr & {\text{ }} = \mathop {\lim }\limits_{x \to {1^ - }} \frac{2}{{\pi \left( {1 - {x^2}} \right){{\sec }^2}\left( {\frac{{\pi x}}{2}} \right)}} \cr & {\text{Evaluate the limit}} \cr & {\text{ }} = \mathop {\lim }\limits_{x \to {1^ - }} \frac{2}{{\pi \left( {1 - {1^2}} \right){{\sec }^2}\left( {\frac{\pi }{2}} \right)}} = \frac{2}{\infty } = 0 \cr & {\text{Therefore}} \cr & \mathop {\lim }\limits_{x \to {1^ - }} \frac{{{{\tanh }^{ - 1}}x}}{{\tan \left( {\pi x/2} \right)}} = 0 \cr} $$
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