## Precalculus (6th Edition) Blitzer

Published by Pearson

# Chapter 5 - Section 5.5 - Trigonometric Equations - Exercise Set - Page 703: 8

#### Answer

$\pi$ is the solution of the given equation.

#### Work Step by Step

We know that according to the ratio table of trigonometry, the value of $\cos \frac{2\pi }{3}$ is given as $-\frac{1}{2}$. \begin{align} & \cos \frac{2x}{3}=-\frac{1}{2} \\ & \cos \frac{2\pi }{3}=-\frac{1}{2} \\ & -\frac{1}{2}=-\frac{1}{2} \end{align} Thus, $\cos \frac{2x}{3}=-\frac{1}{2}$ is true.

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