Primitive of Reciprocal of x squared by Root of x squared plus a squared cubed

Theorem

 * $\displaystyle \int \frac {\mathrm d x} {x^2 \left({\sqrt {x^2 + a^2} }\right)^3} = \frac {-\sqrt {x^2 + a^2} } {a^4 x} - \frac x {a^4 \sqrt {x^2 + a^2} } + C$