Thomas' Calculus 13th Edition

Published by Pearson
ISBN 10: 0-32187-896-5
ISBN 13: 978-0-32187-896-0

Chapter 7: Transcendental Functions - Section 7.5 - Indeterminate Forms and L'Hopital's Rule - Exercises 7.5 - Page 410: 66

Answer

$0$

Work Step by Step

Here, we have $\lim\limits_{x \to 0^{+}} f(x)=\lim\limits_{x \to 0^{+}} \dfrac{\ln x}{\csc x}$ But $\lim\limits_{x \to 0^{+}} \dfrac{\ln x}{\csc x}=\dfrac{\infty}{-\infty}$ This shows an indeterminate form of limit, thus we will apply L-Hospital's rule such as: $\lim\limits_{x \to \infty} f(x)=\lim\limits_{x \to \infty} \dfrac{p'(x)}{q'(x)}$ $\lim\limits_{x \to 0^{+}} \dfrac{1/x}{-\csc x \cot x}=\lim\limits_{x \to 0^{+}} \dfrac{-\sin x \tan x}{x}$ or, $ \dfrac{-\sin 0 \tan 0}{0}=\dfrac{0}{0}$ This shows an indeterminate form of limit, thus we will again apply L-Hospital's rule such as: $\lim\limits_{x \to \infty} f(x)=\lim\limits_{x \to \infty} \dfrac{p'(x)}{q'(x)}$ $\lim\limits_{x \to 0^{+}} \dfrac{(-\cos x)(\tan x)+(-\sin x)(\sec^2 x)}{1}=\dfrac{(-1)(0)+(0)(1)}{1}$ and $\dfrac{0}{1} =0$
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