sin(x-π/2)等于cosx还是-cosx

问题描述:

sin(x-π/2)等于cosx还是-cosx
1.sin(x-π/2)= -sin(π/2-x)= -cos(x) 2.sin(x-π/2)= sin(π-(x-π/2)=sin(π/2-x)=cos(x) 哪一个啊,很像都对啊,

1.sin(x-π/2)= -sin(π/2-x)= -cos(x) 对的 2)sin(x-π/2)= sin(π-(x-π/2)=sin(3π/2-x)=-cos(x)