Solve the following trigonometric equation for $\theta$, where $0\le \theta \le \pi$.
$\cos 2\theta -\cos \theta =0$

$\theta =\{0,\frac{3\pi }{4}\}$

$\theta =\{0,\frac{2\pi }{3}\}$

$\theta =\{\frac{\pi }{6},\frac{5\pi }{6}\}$

$\theta =\{\frac{\pi }{6},\frac{2\pi }{3}\}$