Trigonometry (10th Edition)

Published by Pearson
ISBN 10: 0321671775
ISBN 13: 978-0-32167-177-6

Chapter 5 - Trigonometric Identities - Section 5.2 Verifying Trigonometric Identities - 5.2 Exercises - Page 203: 81

Answer

$\dfrac{\cos{\theta}+1}{\sin{\theta}+\tan{\theta}}=\cot{\theta}$

Work Step by Step

Use agraphing utility to graph $y=\dfrac{\cos{\theta}+1}{\sin{\theta}+\tan{\theta}}$. Refer to the graph below. Notice that the graph looks the same as that of $y=\cot{\theta}$. RECALL: $\tan{\theta}=\dfrac{\sin{\theta}}{\cos{\theta}}\\\\$ Use the definition above to obtain: \begin{align*} \frac{\cos{\theta}+1}{\sin{\theta}+\tan{\theta}}&=\frac{\cos{\theta}+1}{\sin{\theta}+\frac{\sin{\theta}}{\cos{\theta}}}\\\\ &=\frac{\cos{\theta}+1}{\frac{\sin{\theta}\cos{\theta}}{\cos{\theta}}+\frac{\sin{\theta}}{\cos{\theta}}}\\\\ &=\frac{\cos{\theta}+1}{\frac{\sin{\theta}\cos{\theta}+\sin{\theta}}{\cos{\theta}}}\\\\ &=\frac{\cos{\theta}+1}{\frac{\sin{\theta}(\cos{\theta}+1)}{\cos{\theta}}}\\\\ &=(\cos{\theta}+1) \cdot \frac{\cos{\theta}}{\sin{\theta}(\cos{\theta}+1)}\\\\ &=\frac{\cos{\theta}}{\sin{\theta}}\\\\ &=\cot{\theta} \end{align*} Therefore, $$\dfrac{\cos{\theta}+1}{\sin{\theta}+\tan{\theta}}=\cot{\theta}$$
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