I have found this formula and I am trying to prove it , but I have not any idea how to deal with it:
$e^{ax}-e^{bx} = x(a-b)\exp\left[\frac{a+b}{2}x\right]\prod_{i=1}^{\infty}\left[1+\frac{(a-b)^2x^2}{2k^2\pi^{2}}\right] $
It's too complicated for me, any suggestions ?