(1,-1)\(2,1)\(3,7),代入函数y=ax^2+bx+c得
(1)a+b+c=-1.(2)4a+2b+c=1,(3)9a+3b+c=7
(2)-(1)得 (4)3a+b=2,(3)-(1)得 (5)4a+b=4
(5)-(4)得a=2,代入（4）得b=-4,代入（1）得c=1