若cos(a+π/3)=1/4,则sin(a-π/6)的值为
问题描述:
若cos(a+π/3)=1/4,则sin(a-π/6)的值为
答
cos(a+π/3)=
cos(a+π/2-π/6)=-sin(a-π/6)=1/4 所以
sin(a-π/6)=-1/4