Für ${\displaystyle {}x\in \mathbb {R} }$ heißt

${\displaystyle \sum _{n=0}^{\infty }{\frac {(-1)^{n}x^{2n}}{(2n)!}}}$

${\displaystyle \sum _{n=0}^{\infty }{\frac {(-1)^{n}x^{2n+1}}{(2n+1)!}}}$

die Sinusreihe zu ${\displaystyle {}x}$.