Primitive of Reciprocal of x squared minus a squared squared

Theorem

 * $\displaystyle \int \frac {\mathrm d x} {\left({x^2 - a^2}\right)^2} = \frac {-x} {2 a^2 \left({x^2 - a^2}\right)} + \frac 1 {4 a^3} \ln \left\vert{\frac {x + a} {x - a} }\right\vert + C$