∫ sin²x dx = ∫ (1 - cos2x)/2 dx = [x - (1/2)sin2x]/2 + C
∫ sin³x dx = ∫ (cos²x - 1) dcosx = (1/3)cos³x - cosx + C
∫ sin⁴x dx = ∫ [(1 - cos2x)/2]² dx = (1/4)∫ (1 - 2cos2x + cos²2x) dx
= (x - sin2x)/4 + (1/4)∫ (1 + cos4x)/2 dx
= (x - sin2x)/4 + (x + 1/4 • sin4x)/8 + C
= 3x/8 - (1/4)sin2x + (1/32)sin4x + C