Primitive of x cubed over a x + b cubed

Theorem

 * $\displaystyle \int \frac {x^3 \rd x} {\paren {a x + b}^3} = \frac x {a^3} - \frac {3 b^2} {a^4 \paren {a x + b} } + \frac {b^3} {2 a^4 \paren {a x + b}^2} - \frac {3 b} {a^4} \ln \size {a x + b} + C$

Proof
Put $u = a x + b$.

Then:

Then: