sin(3π/2+α)
=sin(π+ π/2+α)
= - sin（π/2+α）
= - cosa
或者 套用公式
sin(3π/2+α)=sin(3π/2）cosa+cos(3π/2）sina= -cosa我知道了 把后面的看成整体是吧是的3π/2+α= π+（ π/2+α）