Primitive of Sine of a x over Sine of a x plus Cosine of a x

Theorem

 * $\displaystyle \int \frac {\sin a x \ \mathrm d x} {\sin a x + \cos a x} = \frac x 2 - \frac 1 {2 a} \ln \left\vert{\sin a x + \cos a x}\right\vert + C$

Proof
First note that:

Then:

Also see

 * Primitive of $\dfrac {\sin a x} {\sin a x - \cos a x}$


 * Primitive of $\dfrac {\cos a x} {\sin a x + \cos a x}$


 * Primitive of $\dfrac {\cos a x} {\sin a x - \cos a x}$