Calculus 10th Edition

Published by Brooks Cole
ISBN 10: 1-28505-709-0
ISBN 13: 978-1-28505-709-5

Chapter 8 - Integration Techniques, L'Hopital's Rule, and Improper Integrals - 8.7 Exercises - Page 564: 48

Answer

$${e^4}$$

Work Step by Step

$$\eqalign{ & \mathop {\lim }\limits_{x \to {0^ + }} {\left( {{e^x} + x} \right)^{2/x}} \cr & {\text{Evaluating the limit}} \cr & \mathop {\lim }\limits_{x \to {0^ + }} {\left( {{e^x} + x} \right)^{2/x}} = {\left( {{e^0} + 0} \right)^{2/{0^ + }}} = {1^\infty } \cr & {\text{This limit has the form }}{1^\infty }{\text{ }} \cr & {\left( {{e^x} + x} \right)^{2/x}} = {e^{\frac{2}{x}\ln \left( {{e^x} + x} \right)}},{\text{ then}} \cr & \mathop {\lim }\limits_{x \to {0^ + }} {\left( {{e^x} + x} \right)^{2/x}} = \mathop {\lim }\limits_{x \to {0^ + }} {e^{\frac{2}{x}\ln \left( {{e^x} + x} \right)}} = {e^{\mathop {\lim }\limits_{x \to {0^ + }} \frac{2}{x}\ln \left( {{e^x} + x} \right)}} \cr & {\text{The first step is to evaluate }} \cr & L = \mathop {\lim }\limits_{x \to {0^ + }} \frac{2}{x}\ln \left( {{e^x} + x} \right) = \mathop {\lim }\limits_{x \to {0^ + }} \frac{{2\ln \left( {{e^0} + 0} \right)}}{0} = \frac{0}{0} \cr & {\text{Using the L'Hopital's rule}} \cr & L = 2\mathop {\lim }\limits_{x \to {0^ + }} \frac{{\frac{d}{{dx}}\left[ {\ln \left( {{e^x} + x} \right)} \right]}}{{\frac{d}{{dx}}\left[ x \right]}} = \mathop {\lim }\limits_{x \to {0^ + }} \frac{{\frac{{{e^x} + 1}}{{{e^x} + x}}}}{1} = \mathop {\lim }\limits_{x \to {0^ + }} \frac{{{e^x} + 1}}{{{e^x} + x}} \cr & = 2\mathop {\lim }\limits_{x \to {0^ + }} \frac{{{e^x} + 1}}{{{e^x} + x}} = 2\left( {\frac{{{e^0} + 1}}{{{e^0} + 0}}} \right) = 2\left( {\frac{2}{1}} \right) = 4 \cr & {\text{Therefore,}} \cr & \mathop {\lim }\limits_{x \to {0^ + }} {e^{\frac{2}{x}\ln \left( {{e^x} + x} \right)}} = {e^{\mathop {\lim }\limits_{x \to {0^ + }} \frac{2}{x}\ln \left( {{e^x} + x} \right)}} = {e^4} \cr & \mathop {\lim }\limits_{x \to {0^ + }} {\left( {{e^x} + x} \right)^{2/x}} = {e^4} \cr} $$
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