Answer
$2k\pi+\frac{\pi}{2}, 2k\pi+\frac{3\pi}{2}$.
$\frac{\pi}{2}, \frac{3\pi}{2}, \frac{5\pi}{2}, \frac{7\pi}{2},\frac{9\pi}{2}, \frac{11\pi}{2}$
Work Step by Step
Using trigonometric identities, we have
$cos(\theta)=0 \longrightarrow \theta=2k\pi+\frac{\pi}{2}, 2k\pi+\frac{3\pi}{2}$.
Six examples $\theta=\frac{\pi}{2}, \frac{3\pi}{2}, \frac{5\pi}{2}, \frac{7\pi}{2},\frac{9\pi}{2}, \frac{11\pi}{2}$