若cos(a-π/3)=3/5 则sin(2a-π/6)=
问题描述:
若cos(a-π/3)=3/5 则sin(2a-π/6)=
答
sin(2a-pi/6)=sin(2(a-pi/3)+pi/2)=cos(2(a-pi/3))=2cos(a-pi/3)*cos(a-pi/3)-1=18/25-1=-7/25
若cos(a-π/3)=3/5 则sin(2a-π/6)=
sin(2a-pi/6)=sin(2(a-pi/3)+pi/2)=cos(2(a-pi/3))=2cos(a-pi/3)*cos(a-pi/3)-1=18/25-1=-7/25