Primitive of Reciprocal of Power of x by Power of x squared plus a squared

Theorem

 * $\displaystyle \int \frac {\mathrm d x} {x^m \left({x^2 + a^2}\right)^n} = \frac 1 {a^2} \int \frac {\mathrm d x} {x^m \left({x^2 + a^2}\right)^{n-1} } - \frac 1 {a^2} \int \frac {\mathrm d x} {x^{m-2} \left({x^2 + a^2}\right)^n}$