(1) 3 = 4a -2b +c
(2) 0 = a + b + c
因为（-2,3）是顶点,所以函数关于X=-2对称.又因为过（1,0）,所以函数还过点（-5,0)
(3) 0 = -25a - 5b + c
(1) - (2) 得
3a - 3b = 3 (4)
(2) - (3) 得
26a + 6b = 0 (5)
2(4) + (5) 得
32a = 6,a = 6/32
则b = -26 / 32,c = 20 / 32
所以y = 6/32 x^2 - 26/32 x + 20/32