y=√3sinx-cosx =2(sinx×√3/2-cosx×1/2) =2(sinxcosπ/6-cosxsinπ/6) =2sin(x-π/6) 所以, y的最小正周期＝2π y的最大值＝2（x=2kπ+2π/3,k为整数）
