Produktentwicklung

$\displaystyle \sin x$	$\displaystyle =$	$\displaystyle x \prod_{k=1}^\infty \left( 1 - \frac{x^2}{k^2\pi^2} \right)$
$\displaystyle \cos x$	$\displaystyle =$	$\displaystyle \prod_{k=1}^\infty \left( 1 - \frac{4x^2}{(2k-1)^2\pi^2} \right)$