分类是一种重要的思想方法,指的是要研究的问题包含多种可能情况,不能一概而就时,我们必须按可能出现的所有情况分别讨论,得出各种情况下相应的结论,并判断其合理性.在解答一些线段或角的求值问题时,要注意认真审题,全面考虑点与线段的位置关系或射线与角的位置关系,分类画出所有符合要求的图形,再分别求值.只有这样,才能得到正确的结论. Classification is an important way of thinking. It means that the problems to be studied contain a variety of possible situations. When they cannot be generalized, we must discuss them separately according to all situations that may arise, and draw conclusions that are relevant in each case. To determine its reasonableness, when answering some line segment or angle evaluation questions, it is necessary to pay attention to careful examination of the problem, to fully consider the positional relationship between points and line segments or the positional relationship between rays and angles, and to draw out all the required patterns and then separately Values. Only in this way can we get the correct conclusion.