Thomas' Calculus 13th Edition

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

Chapter 2: Limits and Continuity - Section 2.4 - One-Sided Limits - Exercises 2.4 - Page 75: 29

Answer

$$\lim _{x \rightarrow 0} \frac{x+x \cos x}{\sin x \cos x}=2$$

Work Step by Step

Given $$\lim _{x \rightarrow 0} \frac{x+x \cos x}{\sin x \cos x}$$ So, we get \begin{aligned}L&=\lim _{x \rightarrow 0} \frac{x+x \cos x}{\sin x \cos x}\\ &=\lim _{x \rightarrow 0} \frac{x(1+ \cos x)}{\sin x \cos x}\\ &=\lim _{x \rightarrow 0}\left(\frac{x}{\sin x} \cdot \frac{1+\cos x}{\cos x}\right)\\ &=\lim _{x \rightarrow 0}\left(\frac{1}{\frac{\sin x}{x}} \cdot \frac{1+\cos x}{\cos x}\right)\\ &=\lim _{x \rightarrow 0} \frac{1}{\frac{\sin x}{x}}.\lim _{x \rightarrow 0} \frac{1+\cos x}{\cos x}\\ &=\frac{\lim _{x \rightarrow 0} 1}{\lim _{x \rightarrow 0} \frac{\sin x}{x}} \cdot \frac{\lim _{x \rightarrow 0}(1+\cos x)}{\lim _{x \rightarrow 0} \cos x}\\ &=\frac{1}{1} \cdot \frac{1+\cos 0}{1}\\ &=1 \cdot 2\\ &=2 \end{aligned}
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