f(x)=√3sin2x+cos2x=2sin(2x+π/6) sin(2x0+π/6)=3/5
Xo属于【π/4,π/2】2x0+π/6∈[2π/3,7π/6] cos(2x0+π/6)=-4/5
cos2Xo=cos[(2x0+π/6)-π/6]=-4√3/10 +3/10=(3-4√3)/10