f(x)=2sinxcos(x +30度)-cos2x+m
=2sinx[(√3/2)cosx-(1/2)sinx]-cos2x+m
=√3sinxcosx-sin²x-cos2x+m
=(√3/2)sin2x-(1-cos2x)/2-cos2x+m
=(√3/2)sin2x-(1/2)cos2x+m-(1/2)
=sin(2x+π/6)+m-1/2
最小正周期为 2π/2=π