Answer
$\theta =\dfrac {\pi }{2}+2\pi k$
$\theta= \dfrac {3\pi }{2}+2\pi k$
Work Step by Step
$\cos \theta \sin \theta -2\cos \theta =0\Rightarrow \cos \theta \left( \sin \theta -2\right) =0$
Since $sin \theta $ can not be 2
$\cos \theta =0\Rightarrow \theta =\cos ^{-1}\left( 0\right) =\dfrac {\pi }{2}+2\pi k;\dfrac {3\pi }{2}+2\pi k$
