f(x)=a*b
=2cos²x-sin²x-(√3)sinxcosx
=cos2x+(1/2)cos2x-(1/2)+((√3)/2)sin2x
=((√3)/2)sin2x+(3/2)cos2x-(1/2)
=(√3)sin(2x+(π/3))-(1/2)
对称轴
2x+(π/3)=kπ+(π/2)
x=(k/2)π+(π/12)