Primitive of x over x fourth minus a fourth

Theorem

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