一元二次方程根的判别式是方程知识的核心内容,是联系3个“二次”(二次函数、二次方程与二次不等式)的重要桥梁.巧用判别式简解数学题,关键在于构造出一元二次方程,然后利用Δ≥0来求解;或构造恒大于等于(或小于等于)0的二次不等式,然后利用Δ≤0来解答.对有些看似与一元二次方程毫无关联的 The discriminant of root of quadratic equation is the core content of equation knowledge and is an important bridge linking three “quadratic ” (quadratic function, quadratic equation and quadratic inequality) , The key is to construct a quadratic equation, and then use Δ ≥ 0 to solve; or construct constant greater than or equal to (or less than or equal to) 0 quadratic inequality, and then use Δ ≤ 0. For some seemingly and quadratic The equation is irrelevant