“判别式法”是初中和高中数学中最常见的一种通法,也是最基本、最重要的一种通法．主要解决有关二次(一元二次方程、一元二次不等式和二次函数)题目中求参数取值范围的问题,但根据通法的局限性,我们必须明确:何时二次问题可以运用“判别式法”,何时不能运用“判别式法”．本文首先给出2个错例和 The “discriminative method” is the most common one in junior high school and high school mathematics. It is also the most basic and important one. It mainly solves the problem of quadratic (universe quadratic equations, quadratic inequalities, and quadratic functions) seeking the range of parameters, but according to the limitations of the common method, we must be clear: when the secondary problem can be used “ ”Discrimination method“, when can’t use ”discriminative method". This article first gives two examples of errors and