以x=-1、y=0代入,得:a-b+c=0 -----------------------------------(1)
以x=3、y=0代入,得:9a+3b+c=0 -----------------------------------(2)
以x=0、y=3/2代入,得:c=3/2 ,代入(1)和(2)中,得:
a-b=-3/2 ==========>>>>>>>> 3a-3b=-9/2 -------------(3)
9a+3b=-3/2 ------------------------------------------------------------(4)
方程(4)-(3),得:
6a=3
a=1/2
将a=1/2代入方程(3)中,得:b=2
所以,y=(1/2)x²+2x-(3/2)