Precalculus (6th Edition)

Published by Pearson
ISBN 10: 013421742X
ISBN 13: 978-0-13421-742-0

Chapter 5 - Trigonometric Functions - 5.3 Trigonometric Functions Values and Angle Measures - 5.3 Exercises - Page 533: 103

Answer

$210^{\circ}$ and $330^{\circ}$

Work Step by Step

$\csc\theta=-2$ $\sin\theta=\frac{1}{\csc\theta}=-\frac{1}{2}$ The value of $\sin \theta$ is negative, so $\theta$ may lie in either quadrant III or IV. We know that $\sin 30^{\circ}=\frac{1}{2}$. Recall: $-\sin x= \sin(180^{\circ}+x)$ and $-\sin x= \sin(360^{\circ}-x)$ $\implies -\sin 30^{\circ}=-\frac{1}{2}=\sin(180^{\circ}+30^{\circ})$ $=\sin 210^{\circ}$ $210^{\circ}$ which is in the third quadrant is one value of $\theta$. Now $-\sin 30^{\circ}=-\frac{1}{2}= \sin (360^{\circ}-30^{\circ})$ $=\sin 330^{\circ}$ $330^{\circ}$ is in the fourth quadrant. The values of $\theta$ are $ 210^{\circ}$ and $330^{\circ}$.
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