Primitive of Reciprocal of p by Sine of a x plus q by Cosine of a x/Lemma

Lemma for Primitive of Reciprocal of p by Sine of a x plus q by Cosine of a x

 * $\ds \frac 1 2 \map \arctan {\dfrac {-p} q} + \frac \pi 4 = \frac {\arctan \dfrac q p} 2$