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二次函数y=ax2+bx+c（a≠0）的图像,若与x轴有两个交点A、B,则|AB|。这是一元二次方程根与系数的第三个关系,其结论可以证明如下:
The image of the quadratic function y=ax2+bx+c(a≠0) has |AB| if it has two intersections A and B with the x-axis. This is the third relationship between the root and coefficient of the quadratic equation, and its conclusion can be proved as follows: