Answer
$-\frac{\sqrt 3}{2}$
Work Step by Step
As $-\frac{7\pi}{6}$ is in quadrant II with a reference angle $\theta=\frac{7\pi}{6}-\pi=\frac{\pi}{6}$, we have $cos(-\frac{7\pi}{6})=-cos(\frac{\pi}{6})=-\frac{\sqrt 3}{2}$
Precalculus (6th Edition)
by Lial, Margaret L.; Hornsby, John; Schneider, David I.; Daniels, Callie
Published by
Pearson
ISBN 10:
013421742X
ISBN 13:
978-0-13421-742-0
Chapter 6 - The Circular Functions and Their Graphs - Test - Page 650: 10
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