一、直线的存在性探究.例1 (2007成都市中考题)在平面直角坐标系xoy中,已知二次函数.y=ax~2+ bx+c(a≠0)的图像与x轴交于A、B两点(点A在点B的左边),与y轴交于点C,其顶点的横坐标为1,且过点(2,3)和(-3,-12).(1)求此二次函数的表达式; First, the existence of the line of inquiry. Example 1 (Chengdu 2007 examination questions) In the plane rectangular coordinate system xoy, known quadratic function. Y = ax ~ 2 + bx + c (a ≠ 0) of the image and the x axis At two points A and B (point A on the left side of point B), intersect with the y-axis at point C, and the abscissa of its vertex is 1, and the points (2,3) and (-3,-12) are crossed. (1) Find the expression of this quadratic function;