$$y=\frac{1+\sin\ x}{1-\sin\ x}$$
$y=-\frac{-\sin(x)-1}{-\sin(x)+1}$
$\nexists n_{1}\in \mathrm{Z}\text{ : }x=2\pi n_{1}+\frac{\pi }{2}$
$y=-\frac{\sin(x)+1}{\sin(x)-1}$
$\nexists n_{1}\in \mathrm{Z}\text{ : }x=2\pi n_{1}+\frac{\pi }{2}$
