P�eme
$$
\sum _{n=0}^{\infty }{\frac {\cos(nx)}{n!}} =
{\it Re}(\sum _{n=0}^{\infty }{\frac {{z}^{n}}
{n!}})={\it Re}({e^{z}}) =
{e
^{\cos(x)}}\cos(\sin(x)) \quad ,
$$
kde $z = \cos (x) + i \sin (x)$.
