✔ 最佳答案
∫ x^2 sin^2(x) cosx dx
=∫ 1/2 x^2 sin2x sinx dx
=1/2 (-1/2) ∫ x^2 (cos3x - cosx) dx
=-1/4 ∫ x^2 cos3x dx +1/4 ∫ x^2 cosx dx
Find ∫ x^2 cos3x dx by part
∫ x^2 cos3x dx = 1/3 sin3x x^2 - 2/3 ∫ xsin3x dx
= 1/3 sin3x x^2 - 2/3 [ -xcos3x / 3 + ∫ cos3x/3 dx]
=1/3 sin3x x^2 +2/9 x cos3x -2/27 sin3x +C
Find ∫ x^2 cosx dx by part
∫ x^2 cosx dx = sinx x^2 - 2∫ x sinx dx
= sinx x^2 -2[-xcosx - ∫ -cosx dx]
=x^2 sinx + 2xcosx - 2sinx + C
so ∫ x^2 sin^2(x) cosx dx = -1/4 [ 1/3 sin3x x^2 +2/9 x cos3x -2/27 sin3x ] +1/4 [x^2 sinx + 2xcosx - 2sinx ]
= -1/12 sin3x x^2 -1/18 x cos3x + 1/54 sin3x +1/4 x^2 sinx + 1/2 x cosx - 1/2 sinx +C
Please tell me if there is a faster method