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.
