一、知识点聚焦1.直线除了“直”的特征外,还有“可向两方无限延伸”的特征,所以直线无“起点”和“终点”(即没有端点).点与直线的位置关系有两种:点在直线上和点在直线外.点在直线上可以说这条直线经过这一点:点在直线外表示这条直线不经过这一点.直线公理“过两点有且只有一条直线”包含两层含义:“有”表示“存在”;“只有”表示“惟一”. First, the focus of knowledge 1. In addition to the characteristics of “straight”, there are “can be extended to the two sides ”features, so there is no “start” and “end” (that is, there is no Endpoints. There are two kinds of positional relationship between points and straight lines: the point is on the straight line and the point is outside the straight line. The point can be said on the straight line this straight line passes this point: the point outside the straight line means the straight line does not pass this point. Axiom “There are two lines and there is only one line ” contains two meanings: “There is ” means “existence ”; “Only ” means “unique”.