Answer
$\theta=k\pi+\frac{\pi}{2}$ (k is an integer),
$\theta=\frac{\pi}{2}, \frac{3\pi}{2},\frac{5\pi}{2},\frac{7\pi}{2},\frac{9\pi}{2},\frac{11\pi}{2}$.
Work Step by Step
$cos\theta=0$,
$\theta=k\pi+\frac{\pi}{2}$ (k is an integer),
Six examples: $\theta=\frac{\pi}{2}, \frac{3\pi}{2},\frac{5\pi}{2},\frac{7\pi}{2},\frac{9\pi}{2},\frac{11\pi}{2}$.
