Answer
$\theta =\dfrac {\pi }{3}+2\pi k $ and $\theta = \dfrac {-\pi}{3}+2\pi k$
Work Step by Step
$4\cos ^{2}\theta -4\cos \theta +1=0\Rightarrow \left( 2\cos \theta -1\right) ^{2}=0\Rightarrow \cos \theta =\dfrac {1}{2}\Rightarrow \theta =\dfrac {\pi }{3}+2\pi k $ and $\theta = \dfrac {-\pi}{3}+2\pi k$
