我们知道 ,抛物线ｙ =ａｘ2 +ｂｘ +ｃ (ａ≠ 0 )是轴对称图形 ,它的对称轴是直线ｘ=-ｂ2ａ,它的顶点在对称轴上 .解决有关抛物线的问题时 ,若能巧用抛物线的对称性 ,则常可以给出简捷的解法 .例 1　已知抛物线的对称轴是ｘ =1 ,抛物线与ｙ轴交于点 (0 ,3) ,与ｘ轴两交点间的距 We know that the parabola y = ax2 + bx + c (a ≠ 0) is an axisymmetric figure whose axis of symmetry is the straight line x = -b2a, whose vertices are on the axis of symmetry. When solving the parabola problem, if With a parabola symmetry, you can often give a simple solution. Example 1 The parabola axis of symmetry is known as x = 1, the parabola intersects the y-axis at points (0, 3), and the distance between the two points of intersection with the x-axis