int x * sin x * cos x dx = 1/2 * int x * 2 * sin x * cos x dx =
= 1/2 * int x * sin 2x dx = 1/2 * int x d(-1/2 * cos 2x) =
= 1/2 * (-1/2) * int x d(cos 2x) = -1/4 * int x d(cos 2x) =
= -1/4 * x * cos 2x + 1/4 * int cos 2x dx =
= -1/4 * x * cos 2x + 1/4 * 1/2 * sin 2x + C =
= -1/4 * x * cos 2x + 1/8 * sin 2x + C