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: 55

Answer

$$1$$

Work Step by Step

$$\eqalign{ & \mathop {\lim }\limits_{x \to {0^ + }} {\left| {\ln x} \right|^x} \cr & {\text{Evaluating}} \cr & \mathop {\lim }\limits_{x \to {0^ + }} {\left| {\ln x} \right|^x} = \mathop {\lim }\limits_{x \to {0^ + }} {\left| {\ln 0} \right|^x} = {\infty ^0} \cr & {\text{This limit has the form }}{\infty ^0}.{\text{ }}\left( {{\text{Using theorem 2}}{\text{.12}}} \right) \cr & {\left| {\ln x} \right|^x} = {e^{x\ln \left( {\ln x} \right)}},{\text{ then}} \cr & \mathop {\lim }\limits_{x \to {0^ + }} {\left| {\ln x} \right|^x} = \mathop {\lim }\limits_{x \to {0^ + }} {e^{x\ln \left( {\ln x} \right)}} = {e^{\mathop {\lim }\limits_{x \to {0^ + }} x\ln \left( {\ln x} \right)}} \cr & {\text{The first step is to evaluate }} \cr & L = \mathop {\lim }\limits_{x \to {0^ + }} x\ln \left( {\ln x} \right) = \mathop {\lim }\limits_{x \to {0^ + }} \frac{{\ln \left( {\ln x} \right)}}{{\frac{1}{x}}} = \frac{\infty }{\infty } \cr & {\text{Using the L'Hopital's rule}} \cr & L = \mathop {\lim }\limits_{x \to {0^ + }} \frac{{\ln \left( {\ln x} \right)}}{{\frac{1}{x}}} = \mathop {\lim }\limits_{x \to {0^ + }} \frac{{\frac{1}{{x\ln x}}}}{{ - \frac{1}{{{x^2}}}}} = - \mathop {\lim }\limits_{x \to {0^ + }} \frac{{{x^2}}}{{x\ln x}} = - \mathop {\lim }\limits_{x \to {0^ + }} \frac{x}{{\ln x}} \cr & - \mathop {\lim }\limits_{x \to {0^ + }} \frac{x}{{\ln x}} = - \mathop {\lim }\limits_{x \to {0^ + }} \frac{x}{{\ln x}} = \frac{0}{\infty } = 0 \cr & {\text{Therefore,}} \cr & \mathop {\lim }\limits_{x \to {0^ + }} {\left| {\ln x} \right|^x} = \mathop {\lim }\limits_{x \to {0^ + }} {e^{x\ln \left( {\ln x} \right)}} = {e^{\mathop {\lim }\limits_{x \to {0^ + }} x\ln \left( {\ln x} \right)}} = {e^0} = 1 \cr & \mathop {\lim }\limits_{x \to {0^ + }} {\left| {\ln x} \right|^x} = 1 \cr} $$
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