Primitive of Reciprocal of Cube of Cosine of a x

Theorem

 * $\displaystyle \int \frac {\mathrm d x} {\cos^3 a x} = \frac {\sin a x} {2 a \cos^2 a x} + \frac 1 {2 a} \ln \left\vert{\tan \left({\frac \pi 4 + \frac {a x} 2}\right)}\right\vert + C$

Also see

 * Primitive of $\dfrac 1 {\sin^3 a x}$