令 x=π/2-t x=0 t =π/2 x=π/2 t=0 dx=-dt 0到π/2 ∫f(sinx)dx=π/2到0 -∫f(cost)dt= 0到π/2∫f(cost)dt x=t dx=dt 0到π/2∫f(cost)dt =0到π/2∫f(cosx)dt x
