一元二次方程ax2＋bx＋c＝0（a≠0）的根的判别式△＝b2－4ac，在中学数学中占有重要的地位．它不仅用于一元二次方程中关于根的讨论，而且在函数、函数的定义域、函数的值域、函数的极值、不等式、因式分解、求变量的变化范围、直线与二次曲线的位置关系等方面都有广泛的应用 The discriminant △=b2-4ac of the root of the one-dimensional quadratic equation ax2+bx+c=0(a≠0) occupies an important position in middle school mathematics. It is not only used for the discussion of roots in quadratic equations, but also in the function, the domain of the function, the value domain of the function, the extremum of the function, inequality, factorization, the variation range of the variable, the straight line and the quadratic curve. Has a wide range of applications such as positional relationships