解由y=2cos^2x-sinxcosx
=2cos^2x-1-1/2*2sinxcosx+1
=cos2x-1/2sin2x+1
=√5/2(2/√5cos2x-1/√5sin2x)+1
=√5/2cos（2x+θ）+1
即最小正周期是T=2π/2=π.