Calculus (3rd Edition)

Published by W. H. Freeman
ISBN 10: 1464125260
ISBN 13: 978-1-46412-526-3

Chapter 7 - Exponential Functions - 7.7 L'Hôpital's Rule - Exercises - Page 366: 38

Answer

$\frac{1}{2}.$

Work Step by Step

We have $$ \lim _{x \rightarrow 1}\frac{x(\ln x-1)+1}{(x-1)\ln x}=\lim _{x \rightarrow 1}\frac{x(\ln x-1)+1}{(x-1)\ln x}=\frac{0}{0} $$ which is an intermediate form, so we can apply L’Hôpital’s Rule as follows $$ \lim _{x \rightarrow 1}\frac{x(\ln x-1)+1}{(x-1)\ln x}=\lim _{x \rightarrow 1}\frac{(\ln x-1)+x(1/x)}{\ln x+(x-1)(1/x)}\\ =\lim _{x \rightarrow 1}\frac{\ln x}{\ln x+1-(1/x)}=\frac{0}{0} $$ which is an intermediate form, so we can apply L’Hôpital’s Rule as follows $$ \lim _{x \rightarrow 1}\frac{\ln x}{\ln x+1-(1/x)}=\lim _{x \rightarrow 1}\frac{1/ x}{1/x+(1/x^2)}=\frac{0}{0} =\frac{1}{2}. $$
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