y=2sin(π/3-a)-cos(π/6+a)=2sinπ/3cosa-2cosπ/3sina-(cosπ/6cosa-sinπ/6sina)=√3cosa-sina-√3/2cosa+1/2sina=√3/2cosa-1/2sina=cos(π/6)cosa-sinπ/6sina=cos(a+π/6)所以-1>=y>=-1所以最小值是y=-1...