降幂再降幂I = (1/4) ∫ (1+cos2x)^2 dx= (1/4) ∫ [1+cos2x+(cos2x)^2] dx= (1/4) ∫ (1+cos2x+1/2+cos4x) dx= (1/4) ∫ (3/2+cos2x+cos4x) dx= (1/4) [(3/2)x + (1/2)sin2x + (1/4)sin4x] + C
很简单，但是我也不会了
