Primitive of Secant of a x/Secant plus Tangent Form

Theorem

 * $\displaystyle \int \sec a x \ \mathrm d x = \frac 1 a \ln \left \vert {\sec a x + \tan a x} \right \vert + C$

where $\sec a x + \tan a x \ne 0$.

Also see

 * Primitive of $\csc a x$: Cosecant minus Cotangent Form