$\left\{\frac{\theta}{\theta}=2 n \pi \pm \frac{\pi}{3}, n \in \mathbf{Z}\right\}$

$\left\{\frac{\theta}{\theta}=n \pi+(-1)^n \frac{\pi}{2}, n \in \mathbf{Z}\right\}$

$\left\{\frac{\theta}{\theta}=n \pi+\frac{\pi}{6}, n \in \mathbf{Z}\right\}$

$\phi$