一、
f(x)=a*b-√3/2
=cosx*√3cosx+sinxcosx-√3/2
=√3cos^2x +sinxcosx-√3/2
=√3/2(cos2x+1)+1/2sin2x-√3/2
=sin(2x+π/3)
所以一条对称轴是 2x+π/3=0 x=-π/6
二、
-5π/12<=x<=π/12
-π/2<=2x+π/3<=π/2
所以f(x)在在区间〖－5π/12,π/12〗上的值域是[-1,1]