Definite Integral to Infinity of Power of x over 1 + 2 x Cosine Beta + x Squared

Theorem

 * $\ds \int_0^\infty \dfrac {x^m \rd x} {1 + 2 x \cos \beta + x^2} = \frac \pi {\sin m x} \frac {\sin m \beta} {\sin \beta}$