y=2cos(x+π/4)*cos(x-π/4)+(√3)sin2x =2sin(π/4-x)*cos(π/4-x)+(√3)sin2x =sin(π/2-2x)+(√3)sin2x =cos2x+(√3)sin2x =2[cosπ/3cos2x+sinπ/3sin2x] =2cos(2x-π/3) 所以,值域[-2,2],周期为π, 2kπ<2x-π/3<(2k+1)π,kπ+π/6
