同学们在初中已经学过了一元二次方程ax2+bx+c=0(a≠0)以及二次函数y=ax2+bx+c(a≠0)的有关知识.仔细观察函数的图象特征,可以发现,如果二次函数的图象与x轴没有交点,那么相应的一元二次方程没有实根;如果函数的图象与x轴只有一个公共点,那么相应的方程只有一个实根(两个相等的实根); The students have learned about the quadratic equation ax2+bx+c=0 (a≠0) and the quadratic function y=ax2+bx+c(a≠0) in junior high school. Look carefully at the image of the function. Characteristic, it can be found that if the image of the quadratic function has no intersection with the x-axis, then the corresponding unary quadratic equation has no real root; if the image of the function has only one common point with the x-axis, the corresponding equation has only one real root. (Two equal real roots);