x^3(cosx)^2属于奇函数，同时积分区间是对称区间，所以积分为0.则原积分=∫(-π/2,π/2)(sinxcosx)^2dx=1/4∫(-π/2,π/2)(sin2x)^2dx=1/8∫(-π/2,π/2)(1-cos4x)dx=1/8*(x-1/4sin4x)|(-π/2,π/2)=π/8
