在圆锥曲线内容的习题教学中,教师都曾有过这样的经历:根据问题给定的条件求直线方程,但是求出后的直线却不存在.直线既然能够求出,又怎么会不存在呢?对此,学生常表现不解与困惑,甚至我们有些教师也知之不多,言之不清.本文结合平时的教学实践,对此谈一点自己的见解与做法,不足 In the conical curricular exercise teaching, teachers have had such an experience: according to the problem given under the conditions of linear equations, but the straight line after the solution does not exist. Since the straight line can be obtained, but also how it does not exist In this regard, students often show puzzled and confused, and even some of our teachers also know little, not clear .This article combined with the usual teaching practice, to talk about their own opinions and practices, inadequate