《圆》是平面几何的最后一章,它包括圆的一些重要性质,直线与圆,圆与圆的相切关系,以及与圆有关的角及比例线段定理。本章的定理、例题和习题,牵涉较多的平面图形知识,综合性也较大。因此,掌握好这一章的教学,不断开拓学生思维,引导学生纵横联想,训练综合应用能力,将对学生智能的培养,取得好的效果。一、重视透彻分析,做以“点”带“片”。例1 如图1,已知圆内接四边形ABCD, “Circle” is the last chapter of plane geometry. It includes some important properties of a circle, the tangent relationship between a circle and a circle, a circle and a circle, and an angle and proportional line segment theorem relating to a circle. The theorems, examples, and exercises in this chapter involve more knowledge of plane graphics and are more comprehensive. Therefore, to master the teaching of this chapter, continue to open up students’ thinking, guide students to think and think, train comprehensive application capabilities, will train students’ intelligence and achieve good results. First, attach importance to thorough analysis and do “points” and “films.” Example 1 As shown in Figure 1, the known circle is inscribed in quadrilateral ABCD,