两条直线被第三条直线所截,构成了八个角,一般称为“三线八角”,如图1,其中没有公共顶点的角可分为三类,即同位角、内错角、同旁内角．它们既是进一步学习直线平行的条件和性质的基础,又是以后学习三角形、相似形、圆等不可缺少的知识．那么怎样才能学好“三线八角”呢? The two straight lines are truncated by the third straight line and form eight corners, which are generally called “three lines and eight horns”. As shown in Figure 1, the angles without common vertices can be divided into three types, ie, the azimuth angle, the internal angle error, and the same Inside corner. They are not only the basis for further study of the conditions and properties of straight-line parallelism, but also the indispensable knowledge for learning triangles, similar shapes, and circles in the future. So how can we learn “three lines and eight horns”?