两条直线被第三条直线所截,图形中共有八个小于180°的角,我们把这个图形称为“三线八角”图,其中没有公共顶点的两个角可以分为三类:同位角、内错角、同旁内角,它们是进一步学习平行线的判定和性质的基础。对学生来说,能否正确区分这三类角,直接影响到对平行线这部分内容的学习。尽管《课程标准》中对于“三线八角”没有明确的描述,但作为学习平行线的必要条件,学生应该熟练地识别同位角、内错角、同旁内角。而识别的 The two straight lines are truncated by the third straight line. There are eight angles less than 180 ° in the drawing. We call this one the “three lines and eight angles” diagram. The two corners without the common vertex can be divided into three categories: The same, the wrong angle, the same angle with the side, they are further learning parallel lines of judgment and nature of the foundation. For students, the correct distinction between these three kinds of angles, a direct impact on the parallel part of this line of learning. Although there is no explicit description of “three lines ” in the Course Standard, as a necessary condition for learning parallel lines, students should be familiar in recognizing the same, opposite, and inner angles. Recognized