integral 6cos4xcos2x dx

InTegraL

∫6 cos 4x cos 2x dx
= 3 ∫2 cos 4x cos 2x dx
= 3 ∫(cos (4x + 2x) + cos (4x - 2x)) dx
= 3 ∫(cos 6x + cos 2x) dx
= 3 (1/6 ∫dsin 6x + 1/2 ∫dsin 2x)
= 1/2 sin 6x + 3/2 sin 2x + C