Answer
$\pi,\frac{\pi}{3},\frac{5\pi}{3}$
Work Step by Step
Step 1. Factor to get $(cos\theta+1)(2cos\theta-1)=0$. Thus $cos\theta=-1$ or $cos\theta=\frac{1}{2}$
Step 2. For $cos\theta=-1$, we have $\theta=\pi$
Step 3. For $cos\theta=\frac{1}{2}$, we have $\theta=\frac{\pi}{3},\frac{5\pi}{3}$
