matematika integral trigonometri ada yang bisa jelasin?

Integration by Substitution.

∫ sin 3x √(cos 3x) dx
Let u = cos 3x, then
du / dx = -3 sin 3x
= ∫ sin 3x √u du / (-3 sin 3x)
= -1/3 ∫ u^(1/2) du
= -1/3 [2/3 u^(3/2)] + C
= -2/9 cos^(3/2) 3x + C
= -2/9 cos 3x √(cos 3x) + C