[1] 将A(2,0)C(0,-1)代入抛物线方程得
2 + 2b + c=0 (i)
c=-1代入 (i)
得 b = -1/2
y =(1/2)x^2 -x/2 -1
[2] 由两点式求得直线AC的方程为y = x/2 -1
设AC上E(x', y') 0
[1] 将A(2,0)C(0,-1)代入抛物线方程得
2 + 2b + c=0 (i)
c=-1代入 (i)
得 b = -1/2
y =(1/2)x^2 -x/2 -1
[2] 由两点式求得直线AC的方程为y = x/2 -1
设AC上E(x', y') 0