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

Theorem

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

Also see

 * Primitive of $\dfrac 1 {\sin a x}$: $\csc - \cot$ form