Calculus: Early Transcendentals (2nd Edition)

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

Chapter 4 - Applications of the Derivative - Review Exercises - Page 331: 53

Answer

$$1$$

Work Step by Step

$$\eqalign{ & \mathop {\lim }\limits_{x \to \pi /{2^ - }} {\left( {\sin x} \right)^{\tan x}} \cr & {\text{Evaluating}} \cr & \mathop {\lim }\limits_{x \to \pi /{2^ - }} {\left( {\sin x} \right)^{\tan x}} = {\left( {\sin \frac{\pi }{2}} \right)^{\tan \pi /2}} = {1^\infty } \cr & {\text{This limit has the form }}{1^\infty }.{\text{ }}\left( {{\text{Using theorem 2}}{\text{.12}}} \right) \cr & {\text{Nothing that }}{\left( {\sin x} \right)^{\tan x}} = {e^{\tan x\ln \sin x}},{\text{ then}} \cr & \mathop {\lim }\limits_{x \to \pi /{2^ - }} {\left( {\sin x} \right)^{\tan x}} = \mathop {\lim }\limits_{x \to {0^ + }} {e^{\tan x\ln \sin x}} = {e^{\mathop {\lim }\limits_{x \to \pi /{2^ - }} \left( {\tan x\ln \sin x} \right)}} \cr & {\text{The first step is to evaluate }} \cr & L = \mathop {\lim }\limits_{x \to \pi /{2^ - }} \left( {\tan x\ln \sin x} \right) = \mathop {\lim }\limits_{x \to \pi /{2^ - }} \frac{{\ln \sin x}}{{\frac{1}{{\tan x}}}} = \mathop {\lim }\limits_{x \to \pi /{2^ - }} \frac{{\ln \sin x}}{{\cot x}} \cr & L = \mathop {\lim }\limits_{x \to \pi /{2^ - }} \frac{{\ln \sin x}}{{\cot x}} = \frac{0}{0} \cr & {\text{Using the L'Hopital's rule}} \cr & L = \mathop {\lim }\limits_{x \to \pi /{2^ - }} \frac{{\ln \sin x}}{{\cot x}} = \mathop {\lim }\limits_{x \to \pi /{2^ - }} \frac{{\cos x}}{{ - {{\csc }^2}x}} \cr & \mathop {\lim }\limits_{x \to \pi /{2^ - }} \frac{{\cos x}}{{ - {{\csc }^2}x}} = \frac{{\cos \left( {\pi /2} \right)}}{{ - {{\csc }^2}\left( {\pi /2} \right)}} = \frac{0}{{ - 1}} = 0 \cr & {\text{Therefore,}} \cr & \mathop {\lim }\limits_{x \to \pi /{2^ - }} {\left( {\sin x} \right)^{\tan x}} = \mathop {\lim }\limits_{x \to {0^ + }} {e^{\tan x\ln \sin x}} = {e^{\mathop {\lim }\limits_{x \to \pi /{2^ - }} \left( {\tan x\ln \sin x} \right)}} = {e^0} = 1 \cr & \mathop {\lim }\limits_{x \to \pi /{2^ - }} {\left( {\sin x} \right)^{\tan x}} = 1 \cr} $$
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