Precalculus (6th Edition)

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

Chapter 7 - Trigonometric Identities and Equations - Chapter 7 Test Prep - Review Exercises - Page 738: 76


$y=\displaystyle \frac{2\pi}{3}$

Work Step by Step

By definition of arccos, y is the number from $[0, \pi]$ such that $\displaystyle \cos y=-\frac{1}{2}.$ Using the unit circle, we find that $\displaystyle \frac{2\pi}{3}\in[0, \pi] $and $\displaystyle \cos\frac{2\pi}{3}=-\frac{1}{2}.$ $y=\displaystyle \frac{2\pi}{3}$
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