f(x)=2cos^2x/2-根号3sinx
=1+cosx-√3sinx
=1+2(1/2*cosx-√3/2*sinx)
=1+2sin(π/6-x)
当sin(π/6-x)=1时,f(x)max=3
当sin(π/6-x)=-1时,f(x)min=-1