分类讨论是每年高考考查的重要思想方法之一 ,一些文章对此作了大量的探讨 ,中学教师在教学中更是反复渗透 ,多次训练 .通过指导与训练 ,大部分学生基本上能运用这一思想方法解决一些问题 ,但总有一部分学生 (包括一些成绩优秀的学生 )在分类讨论求得某个字母的取值范围之后 , Classification discussion is one of the important ideas and methods for the annual college entrance examination examination. Some articles have made a lot of discussion on this. Middle school teachers are repeatedly infiltrated and trained many times. Through guidance and training, most students can basically use this. A way of thinking to solve some problems, but there are always a part of students (including some outstanding students) after the classification discussion to obtain a range of values ​​of a letter,