Parseval's Integral

The Poisson Integral with $n=0$.

$$J_0(z)={1\over[\Gamma(n+{\textstyle{1\over 2}})]^2} \int_0^\pi \cos(z\cos\theta)\,d\theta,$$

where $J_0(z)$ is a Bessel Function of the First Kind and $\Gamma(x)$ is a Gamma Function.