= \sum\limits_{k \in \mathbb{Z}} {P\left( {k\pi - \frac{\pi }
{2} \leqslant Y \leqslant k\pi + \arctan z} \right)} = \sum\limits_{k \in \mathbb{Z}} {\int_{k\pi - \frac{\pi }
{2}}^{k\pi + \arctan z} {f_Y \left( y \right)dy} } =