Se�t�te mocninnou �adu
$$
\sum _{n=1}^{\infty }{\frac {\left (-1\right )^{n}{
x}^{2\,n+1}n}{\left (2\,n+1\right )!}}=-{\frac {
\sin(x)}{2}}+{\frac {\cos(x)x}{2}} \quad .
$$

