△ =b2 - 4ac叫做一元二次方程 ax2 + bx+ c=0的根的判别式。它的取值大小决定着一元二次方程 ax2 + bx+ c=0实根的有无及多少。灵活运用它可使一些几何问题的解答变得简易、迅捷。在这种方法中 ,应注意根据几何图形的性质 ,构造关于某一几何量为元的一元二次方程。例 1.如图 , △ = b2 - 4ac is the discriminant of the root of a quadratic equation ax2 + bx + c=0. Its size determines the presence or absence of the real root of the one-member quadratic equation ax2 + bx + c = 0. Using it flexibly can make the solution of some geometric problems easy and quick. In this method, it should be noted that according to the nature of the geometry, a quadratic equation with a certain amount of geometry is constructed. Example 1. Figure,