integral 12 cos 4x cos 2x

jawab
∫ 12 cos 4x cos 2x dx
= 6 ∫ 2 cos 4x cos 2x dx
= 6 ∫ cos (4x+2x) + cos(4x-2x) dx
= 6 ∫ cos 6x + cos 2x dx
= 6 [ 1/6 sin 6x + 1/2 sin 2x ] +c
= sin 6x + 3 sin 2x + c