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: 57

Answer

$$ \lim _{x \rightarrow 0^{+}} x^{\sqrt x}=1 $$

Work Step by Step

$$ \lim _{x \rightarrow 0^{+}} x^{\sqrt x} $$ Let $$ y=x^{\sqrt x} $$ Then $$ \ln y= \sqrt{x} \ln x= \frac{\ln x}{x^{-1 / 2}} $$ notice that as $ \quad x \rightarrow 0^{+} \quad $ we have $ \quad \ln x \rightarrow \infty \quad $ and $ \quad x^{-1 / 2} \rightarrow \infty $ so l’Hospital’s Rule gives $$ \begin{aligned} \lim _{x \rightarrow 0^{+}} \ln y & =\lim _{x \rightarrow 0^{+}} \sqrt{x} \ln x \\ & =\lim _{x \rightarrow 0^{+}} \frac{\ln x}{x^{-1 / 2}} \quad \rightarrow \frac{\infty}{\infty}\\ & \stackrel{\mathrm{H}}{=} \lim _{x \rightarrow 0^{+}} \frac{1 / x}{-\frac{1}{2} x^{-3 / 2}} \\ & =-2 \lim _{x \rightarrow 0^{+}} \sqrt{x} \\ &=0 \end{aligned} $$ Hence, we have $$ \begin{aligned} \lim _{x \rightarrow 0^{+}} x^{\sqrt{x}} &=\lim _{x \rightarrow 0^{+}} e^{\ln y} \\ &=e^{0}\\ &=1 \end{aligned} $$
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