判断两条直线是否平行,既是已学知识的延续和提高,又是继续学习不可缺少的基础,其关键是弄清楚这两条直线被哪一条直线所截；所截得的一对角是同位角、内错角还是同旁内角,然后再根据直线平行的条件加以判断．为帮助同学们更好地掌握这部分知识,提高同学们的思考和表达能力,现举例解析,供同学们参考． Judging whether two straight lines are parallel is not only a continuation and improvement of the learned knowledge, but also an indispensable foundation for continuing learning. The key is to find out which straight line the two straight lines are cut in; the intercepted pair of corners is the same position. The angle, the inner angle or the inner angle, and then judged according to the conditions of the straight line parallel. In order to help the students to better grasp this part of the knowledge and improve the students’ thinking and expression skills, this is an example analysis for the students to refer to.