Mathematics

Problem

For

0\le x\le 2\pi

, the solutions of

\cos x\cos\frac{\pi}{6}-\sin x\sin\frac{\pi}{6}=-\frac{\sqrt3}{2}

are a)

x=\dfrac{\pi}{3},\;\dfrac{5\pi}{3}

x=\dfrac{5\pi}{6},\;\dfrac{7\pi}{6}

x=\dfrac{2\pi}{3},\;\pi

x=\pi,\;\dfrac{4\pi}{3}