f(x)=2sin2xcos(π/6)-cos2x+a
=2sin2xcos(π/6)-2cos2xsin(π/6)+a
=2sin(2x-π/6)+a
最小正周期T=2π/2=π
单调减区间为：2kπ+π/2=ͼƬ���Բ����������ĵ㿴���壿