由对称性可知:A(1,0),B(3,0), E(-1,0)与x轴交槐尘羡点铅拍为B(3,0), E(-1,0),经过C(0,2)y=a(x+1)(x-3)a(0+1)(0-3)=2a=-2/兄扒3y=-2/3(x+1)(x-3)=-2/3x^2+4/3+2y=-2/3x^2+4/3+2
用假设法试试呢?