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）