Primitive of Reciprocal of Root of x squared minus a squared/Logarithm Form

Theorem

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

Also see

 * Primitive of Reciprocal of $\sqrt {x^2 + a^2}$: Inverse Hyperbolic Sine Form