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: 42

Answer

$$1$$

Work Step by Step

\begin{align*} \lim _{\theta \rightarrow 0} \frac{\theta \cot 4 \theta}{\sin ^{2} \theta \cot ^{2} 2 \theta}&=\lim _{\theta \rightarrow 0} \frac{\theta^{\cos 4 \theta}}{\sin ^{2} \theta \frac{\cos ^{2} 2 \theta}{\sin ^{2}2 \theta}}\\ &=\lim _{\theta \rightarrow 0} \frac{\theta \cos 4 \theta \sin ^{2} 2 \theta}{\sin ^{2} \theta \cos ^{2} 2 \theta \sin 4 \theta}\\ &=\lim _{\theta \rightarrow 0} \frac{\theta \cos 4 \theta(2 \sin \theta \cos \theta)^{2}}{\sin ^{2} \theta \cos ^{2} 2 \theta \sin 4 \theta}\\ &=\lim _{\theta \rightarrow 0} \frac{\theta \cos 4 \theta\left(4 \sin ^{2} \theta \cos ^{2} \theta\right)}{\sin ^{2} \theta \cos ^{2} 2 \theta \sin 4 \theta}\\ &=\lim _{\theta \rightarrow 0} \frac{4 \theta \cos 4 \theta \cos ^{2} \theta}{\cos ^{2} 2 \theta \sin 4 \theta}\\ &=\lim _{\theta \rightarrow 0}\left(\frac{4 \theta}{\sin 4 \theta}\right)\left(\frac{\cos 4 \theta \cos ^{2} \theta}{\cos ^{2} 2 \theta}\right)\\ &=\lim _{\theta \rightarrow 0}\left(\frac{1}{\frac{\sin 4 \theta}{4 \theta}}\right)\left(\frac{\cos 4 \theta \cos ^{2} \theta}{\cos ^{2} 2 \theta}\right)\\ &=\left(\frac{1}{1}\right)\left(\frac{1-1^{2}}{1^{2}}\right)=1 \end{align*}
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