Calculus 8th Edition

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

Chapter 6 - Inverse Functions - Review - Exercises - Page 506: 77

Answer

$$ \lim _{x \rightarrow 1^{+}}\left(\frac{x}{x-1}-\frac{1}{\ln x}\right) =\frac{1}{2} $$

Work Step by Step

$$ \lim _{x \rightarrow 1^{+}}\left(\frac{x}{x-1}-\frac{1}{\ln x}\right) $$ First notice that $$ \lim _{x \rightarrow 1^{+}} \frac{x}{x-1} \,\,\, \rightarrow \infty $$ and $$ \lim _{x \rightarrow 0^{+}} \frac{1}{\ln x}\,\,\, \rightarrow \infty , $$ so the limit is indeterminate and has the form $\infty -\infty $. Here we use a common denominator and l’Hospital’s Rule is justified, then we gives: $$\begin{aligned} \lim _{x \rightarrow 1^{+}}\left(\frac{x}{x-1}-\frac{1}{\ln x}\right) &=\lim _{x \rightarrow 1^{+}}\left(\frac{x \ln x-x+1}{(x-1) \ln x}\right) \rightarrow \frac{0}{0} \\ & \stackrel{\mathrm{H}}{=} \lim _{x \rightarrow 1^{+}} \frac{x \cdot(1 / x)+\ln x-1}{(x-1) \cdot(1 / x)+\ln x} \\ &=\lim _{x \rightarrow 1^{+}} \frac{\ln x}{1-1 / x+\ln x} \rightarrow \frac{0}{0} \\ & \stackrel{\mathrm{H}}{=} \lim _{x \rightarrow 1^{+}} \frac{1 / x}{1 / x^{2}+1 / x} \\ &=\frac{1}{1+1} \\ &=\frac{1}{2}. \end{aligned}$$
Update this answer!

You can help us out by revising, improving and updating this answer.

Update this answer

After you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.