$$\frac{ 1+ \sin \theta - \cos \theta }{ 1+ \sin \theta + \cos \theta } + \frac{ 1+ \sin \theta + \cos \theta }{ 1+ \sin \theta + \cos \theta } =2 \csc \theta$$
$\theta =2\pi n_{1}+\frac{\pi }{2}$
$n_{1}\in \mathrm{Z}$
