Answer
$\theta = 90^{\circ},270^{\circ} $
Work Step by Step
$2 \cos{\theta} - 2 \cos{\theta} \sin{\theta} = 0$
$\cos{\theta} - \cos{\theta} \sin{\theta} = 0$
$\cos{\theta} (1 - \sin{ \theta}) = 0$
$\cos{\theta} = 0 \hspace{30pt} \text{ or } \hspace{30pt} (1-\sin{\theta}) = 0$
$\cos{\theta} = 0 \hspace{30pt} \text{ or } \sin{\theta} = 1$
$\theta = 90^{\circ},270^{\circ} \hspace{30pt} \theta = 90^{\circ}$
$\therefore \theta = 90^{\circ},270^{\circ} $
