Primitive of Fourth Power of Cosine of a x

Theorem

 * $\displaystyle \int \cos^4 a x \ \mathrm d x = \frac {3 x} 8 + \frac {\sin 2 a x} {4 a} + \frac {\sin 4 a x} {32 a} + C$

Also see

 * Primitive of $\sin^4 a x$