Primitive of Reciprocal of a squared minus x squared/Logarithm Form 1/size of x greater than a

Theorem
Let $a \in \R_{>0}$ be a strictly positive real constant. Let $\size x > a$.

Then:
 * $\displaystyle \int \frac {\d x} {a^2 - x^2} = \dfrac 1 {2 a} \ln \size {\dfrac {x + a} {x - a} } + C$