Trigonometry (11th Edition) Clone

Published by Pearson
ISBN 10: 978-0-13-421743-7
ISBN 13: 978-0-13421-743-7

Chapter 3 - Radian Measure and the Unit Circle - Section 3.1 Radian Measure - 3.1 Exercises - Page 105: 84



Work Step by Step

Convert the angle measure to degrees to obtain: $=-\frac{\pi}{6} \cdot \frac{180^o}{\pi} = -30^o$ Thus, $\cos{(-\frac{\pi}{6})} = \cos{(-30^o)}$ $-30^o$ is co-terminal with $-30^o+360^o=330^o$. $330^o$ is in Quadrant IV so its reference angle is $=360^o-330^o=30^o$. Note that the cosine function is positive in Quadrant IV.
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