y=1/2(2cosx^2+根号3*2sinxcosx+2)
=1/2(2cosx^2-1+根号3*2sinxcosx+3)
=1/2(cos2x+根号3sin2x+3)
=1/2cos2x+根号3/2*sin2x+3/2
=sin(2x+π/6)+3/2
接下来的自己算