Primitive of Cosine of a x by Cosine of p x

Theorem

 * $\ds \int \cos a x \cos p x \rd x = \frac {\map \sin {\paren {a - p} x} } {2 \paren {a - p} } + \frac {\map \sin {\paren {a + p} x} } {2 \paren {a + p} } + C$

Also see

 * Primitive of $\sin p x \sin q x$
 * Primitive of $\sin p x \cos q x$