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 502: 97

Answer

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

Work Step by Step

$$ \begin{aligned} L& = \lim _{x \rightarrow \infty}\left[x-x^{2} \ln \left(\frac{1+x}{x}\right)\right] \\ &=\lim _{x \rightarrow \infty}\left[x-x^{2} \ln \left(\frac{1}{x}+1\right)\right] \\ & \quad \quad \quad \left[ \text { Let } t=1 / x, \text { so as } x \rightarrow \infty, t \rightarrow 0^{+} , \text { then}\right] \\ &=\lim _{t \rightarrow 0^{+}}\left[\frac{1}{t}-\frac{1}{t^{2}} \ln (t+1)\right]\\ &=\lim _{t \rightarrow 0^{+}} \frac{t-\ln (t+1)}{t^{2}} \\ & \quad \quad \left[ \text { notice that as } t \rightarrow 0^{+} \text { we have} \quad (t-\ln (t+1)) \rightarrow 0 \quad \text {and} \quad t^{2} \rightarrow 0. \quad \text {This gives an indeterminate form of the type } \frac{0}{0} \\\text {so l’Hospital’s Rule gives} \right] \\ &\stackrel{\mathrm{H}}{=} \lim _{t \rightarrow 0^{+}} \frac{1-\frac{1}{t+1}}{2 t} \\ &=\lim _{t \rightarrow 0^{+}} \frac{t /(t+1)}{2 t} \\ &=\lim _{t \rightarrow 0^{+}} \frac{1}{2(t+1)} \\ &=\frac{1}{2}. \end{aligned} $$
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.