cos(3π/2－x)=cos(3π/2)cosx＋sin(3π/2)sinx=－sinx
则：
－sinx=cos(3π/2－x)从-sinx推导下－sinx=0cosx－sinx=cos(3π/2)cosx＋sin(3π/2)sinx=cos(3π/2－x)