# Primitive of Reciprocal of Root of x squared minus a squared

## Theorem

### Inverse Hyperbolic Cosine Form

$\ds \int \frac {\d x} {\sqrt {x^2 - a^2} } = \dfrac {\size x} x \arcosh {\size {\frac x a} } + C$

for $x^2 > a^2$.

### Logarithm Form

$\ds \int \frac {\d x} {\sqrt {x^2 - a^2} } = \ln \size {x + \sqrt {x^2 - a^2} } + C$