由抛物线过X轴上的点A、C,可设其解析式是y=a(x-1)(x-3)
将B（-3,4）代入,得
a(-3-1)(-3-3)=4
24a=4
a=1/6
∴函数解析式是y=(1/6)(x-1)(x-3)
=(1/6)(x²-4x+3)
=(1/6)x²-(2/3)X+½