# Question #ec67a

$\sin x \cos 2 x + \sin 2 x \cos x = 0 \implies \sin \left(x + 2 x\right) = 0 \implies \sin 3 x = 0$
$\sin 3 x = 0 \implies x = k \cdot \frac{\pi}{3}$ where $k$ is an integer