原式=∫[(sinθ)^2]^2dθ=∫[(1-cos2θ)/2]^2dθ=(1/4)∫[1-2cos2θ+(cos2θ)^2]dθ=θ/4-(1/4)∫cos2θd(2θ)+(1/4)∫[1+cos4θ)/2]dθ=θ/4-(sin2θ)/4+θ/8+(1/8)(1/4)sin4θ+C=3θ/8-(1/4)sin2θ+(1/32)sin4θ+C...