cos(a+派/6)-sina=3根号3/5,则cos(a+派/3)=?

cos(a+π/6)-sina=cosa*cos(π/6)-sina*sin(π/6)-sina=√3/2 cosa-3/2sina=3/5*√3
cos(a+π/3)=cosa*cos(π/3)-sina*sin(π/3)=1/2 cosa-√3/2 sina=[cos(a+π/6)-sina]/√3=3/5