y=cosx(sinx-√3cosx)+√3/2
=cosxsinx-√3(cosx)^2+√3/2
=sin2x/2-√3cos2x/2
=sin(2x-π/3)
当x=-π/2时y=sin(-π-π/3)=sinπ/3=√3/2
当x=0时y=sin(-π/3)=-√3/2