Algebra and Trigonometry 10th Edition

Published by Cengage Learning
ISBN 10: 9781337271172
ISBN 13: 978-1-33727-117-2

Chapter 6 - Chapter Test - Page 503: 8


$\theta=120°$ $\theta=240°$

Work Step by Step

Let $\theta'$ be a refernce angle such that $\theta'$ lies in the first quadrant and: $cos~\theta'=\frac{\sqrt 3}{2}$ Then: $\theta'=60°$ If $cos~\theta\lt0$, then $\theta$ lies in the second or in the third quadrant: $\theta=180°-\theta'=180°-60°=120°$ or $\theta=180°+\theta'=180°+60°=240 °$
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