Calculus 8th Edition

Published by Cengage
ISBN 10: 1285740629
ISBN 13: 978-1-28574-062-1

Chapter 6 - Inverse Functions - 6.8 Indeterminate Forms and I'Hospital's Rule - 6.8 Exercises - Page 500: 63

Answer

$$ \lim _{x \rightarrow \infty} x^{1 / x}=1 $$

Work Step by Step

$$ \lim _{x \rightarrow \infty} x^{1 / x} $$ Let $$ y= x^{1 / x} $$ Then $$ \ln y=(1 / x) \ln x =\frac{ \ln x}{x} $$ notice that as $ \quad x \rightarrow \infty \quad $ we have $ \quad \ln x \rightarrow \infty \quad $ and $ \quad x \rightarrow \infty $ so l’Hospital’s Rule gives $$ \begin{aligned} \lim _{x \rightarrow \infty} \ln y &=\lim _{x \rightarrow \infty} \frac{\ln x}{x} \quad\quad \rightarrow \frac{\infty}{\infty}\\ & \stackrel{\mathrm{H}}{=} \lim _{x \rightarrow \infty} \frac{1 / x}{1} \\ &=0 \end{aligned} $$ Hence, we have $$ \begin{aligned} \lim _{x \rightarrow \infty} x^{1 / x} &=\lim _{x \rightarrow \infty} e^{\ln y} \\ &=e^{0} \\ &=1 \end{aligned} $$
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