第13課 这节課教学垂線和斜線(§26)。为了巩固上节課所講的教材,这节課在开始的时候,可以多花費一些时間进行复習,例如提問学生:怎样的角叫做鄰补角、对頂角?同角的鄰补角的性質怎样?为什么?对顶角的性質怎样?为什么?另外可以从上节課的复習巩固材料中选取几題进行提問。最后提問:“兩条直 Lesson 13 This lesson teaches vertical and oblique lines (§26). In order to consolidate the teaching materials taught in the previous class, at the beginning of this class, you can spend more time reviewing, for example, asking students: What angles are called adjoining corners, adjoining corners, and adjoining corners in the same corner? What is the nature, why? What is the nature of the vertex angle and why? Another question can be selected from the review of the last section of the consolidating material. Last question: "Two straight