Primitive of Reciprocal of x squared plus a squared/Arctangent Form

Theorem

 * $\displaystyle \int \frac {\d x} {x^2 + a^2} = \frac 1 a \arctan \frac x a + C$

where $a$ is a non-zero constant.

Also see

 * Derivative of Arctangent Function


 * Primitive of Reciprocal of $x^2 - a^2$
 * Primitive of Reciprocal of $a^2 - x^2$