## Algebra 2 (1st Edition)

$x=\dfrac{\pi}{3}, \dfrac{2 \pi}{3}, \dfrac{4 \pi}{3}, \dfrac{ 5\pi}{3}$
Use the identity double angle formula: $2 \cos^2 x-1=-2 \cos^2 x$ Then, we have $4 \cos^2 x-1 =0$ $\implies \cos^2 x=\dfrac{1}{4}$ Here, $\cos x=\dfrac{1}{2}$ and $\cos x=- \dfrac{1}{2}$ Thus, we have $x=\dfrac{\pi}{3}, \dfrac{2 \pi}{3}, \dfrac{4 \pi}{3}, \dfrac{ 5\pi}{3}$