Primitive of Reciprocal of Cosine of a x/Logarithm of Tangent Form

Theorem

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

Also see

 * Primitive of $\dfrac 1 {\sin a x}$: $\tan$ form