Trigonometric Equations

$x=2 \mathrm{n} \pi, \mathrm{n} \in \mathbb{Z}$

$x=\mathrm{n} \pi+\frac{\pi}{2}, \mathrm{n} \in \mathbb{Z}$

$x=\mathrm{n} \pi+(-1)^{\mathrm{n}} \frac{\pi}{4}-\frac{\pi}{4}, \mathrm{n} \in \mathbb{Z}$

not existing