已知sin(x-15°)=1/3,求cos(30°一2x)
问题描述:
已知sin(x-15°)=1/3,求cos(30°一2x)
答
cos(30-2x)=cos(2x-30)=1-2sin(x-15)^2=7/9
已知sin(x-15°)=1/3,求cos(30°一2x)
cos(30-2x)=cos(2x-30)=1-2sin(x-15)^2=7/9