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: 32

Answer

\[ \lim_{x\rightarrow \infty}\frac{(\ln x)^2}{x}=0\]

Work Step by Step

Let \[l=\lim_{x\rightarrow \infty}\frac{(\ln x)^2}{x}\] Which is $\frac{\infty}{\infty}$ form Using L'Hopital's rule \[l=\lim_{x\rightarrow \infty}\frac{\{(\ln x)^2\}'}{(x)'}\] \[\Rightarrow l= \lim_{x\rightarrow \infty}\frac{2\ln x\cdot\frac{1}{x}}{1}\] \[\Rightarrow l=\lim_{x\rightarrow \infty}\frac{2\ln x}{x}\] Which is again $\frac{\infty}{\infty}$ form Using L'Hopital's rule \[\Rightarrow l=\lim_{x\rightarrow \infty}\frac{(2\ln x)'}{(x)'}\] \[\Rightarrow l=\lim_{x\rightarrow \infty}\frac{2}{x}\] \[\Rightarrow l=0\] Hence ,\[ \lim_{x\rightarrow \infty}\frac{(\ln x)^2}{x}=0\]
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