f(x)=√3/2sin2x-(1+cos2x)/2-1/2
=√3/2sin2x-1/2cos2x-1
=sin(2x-π/6)-1
当sin(2x-π/6)=-1时,f(x)取最小值-2
此时2x-π/6=2kπ-π/2,得：x=kπ-π/6