Primitive of Reciprocal of p squared by square of Sine of a x plus q squared by square of Cosine of a x

Theorem

 * $\displaystyle \int \frac {\mathrm d x} {p^2 \sin^2 a x + q^2 \cos^2 a x} = \frac 1 {a p q} \arctan \left({\frac {p \tan a x} q}\right) + C$