Primitive of x cubed over Root of x squared plus a squared cubed

Theorem

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