分类讨论思想是以概念的划分、集合的分类为基础的思想方法.它是为了解决因各种因素制约着的数学问题,使原本变幻的不定的问题,分解成若干个相对确定的问题,再各个击破,从而获得完整的解答.分类讨论必须遵循三条原则:一是对全体分类对象做到“既不重复,也不遗漏”,二是每次分类 The idea of ​​classification and discussion is based on the division of concepts and the classification of collections. It is to solve mathematical problems that are constrained by various factors, and to decompose the indefinite problems of the original into several relatively definite problems. Each break, in order to obtain a complete solution. Category discussion must follow three principles: First, to achieve the entire classification object “neither repeat, nor omission”, and second, each classification