Primitive of Reciprocal of a squared minus x squared/Inverse Hyperbolic Tangent Form

Theorem

 * $\ds \int \frac {\d x} {a^2 - x^2} = \frac 1 a \tanh^{-1} \frac x a + C$

where $\size x < a$.

Also see

 * Primitive of $\dfrac 1 {x^2 - a^2}$: $\coth^{-1}$ form for the case $\size x > a > 0$