1.怎样理解线段的定义? 答:线段是在直线概念的基础上定义的,直线上两个点和它们之间的部分叫线段。 2.怎样表示线段? 答:线段有两种常用的表示方法:一是用表示其两个端点的大写字母来表示;二是用一个小写字母来表示。如图1,既可记作线段AB或线段BA,也可记作线段l。注意:不能用一个大写字母或一个大写字母和一个小写字母 1. How to understand the definition of the line segment? A: The line segment is defined on the basis of the straight line concept. The two points on the line and the part between them are called line segments. 2. How to represent segments? Answer: There are two common representations of line segments: one is capital letters that represent the two endpoints, and the other is a lowercase letter. As shown in FIG. 1 , it can be recorded as a line segment AB or a line segment BA, or as a line segment l. Note: You cannot use a capital letter or an uppercase letter and a lowercase letter