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表示线段,也不能用两个小写字母表示线段. 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 express the line segment? A: There are two common expressions of the line segment. Method: First, use uppercase letters to represent its two endpoints; Second, use a lowercase letter to represent. As shown in Figure 1, can be recorded as line segment AB or line segment BA, can also be recorded as line segment l. Note: can not be used A capital letter or an uppercase letter and a lowercase letter represent line segments. Line segments cannot be represented by two lower case letters.