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抛物线y=ax2+bx+c(a≠0),当Δ=b2-4ac>0时,它与x轴必有不同的两个交点,此两点间的距离叫做抛物线截x轴所得弦长.巧妙抓住这一弦长,有时可使许多抛物线问题获得十分快捷的解法.让我们先看如下简单性质:
The parabola is y=ax2+bx+c(a≠0). When Δ=b2-4ac>0, it must have two different intersections with the x-axis. The distance between these two points is called the parabola-cut x-axis. Cleverly grasping this chord length can sometimes make many parabolic problems get a very quick solution. Let us first look at the following simple properties: