初三 ( 4)班的数学课外活动小组为了深入探讨二次函数解析式的简捷求法 ,召开了一次专题讨论会 .组长张翔 :二次函数解析式的求法灵活性较大 .如何根据题目的已知条件 ,选择最简捷的方法求解 ,请同学们各抒己见 .例 1　已知抛物线ｙ =ａｘ2 +ｂｘ +ｃ的顶点为 ( 2 ,0 )且过点 ( The group of mathematics extracurricular activities of the third grade (4) class held a symposium in order to deeply discuss the simple and straightforward method of solving the quadratic function analysis. The leader Zhang Xiang: The quadratic function analytical method has greater flexibility in the method. How to solve the problem For the known conditions, choose the simplest method to solve, and ask the students to express their own opinions. Example 1 The vertex y = ax2 + bx +c is known to have a vertex of (2, 0) and cross the point (