圆与圆的位置关系这一单元 ,两圆相交和相切是重点 在这一单元中有几道证明两线平行的题目 ,通过这几道题目的变式训练 ,可以把两圆相交和相切中辅助线的作法 ,证明命题的方法让学生掌握清楚 已知 :如图 1,⊙Ｏ1 与⊙Ｏ2 相交与Ａ ,Ｂ两点 ,分别过Ａ ,Ｂ两点作直线交⊙Ｏ1 于 The unit of the relationship between circle and circle, the intersection and tangency of the two circles are the focus of the problem in this unit. There are several lines that prove the parallelism of the two lines. Through the variant training of these several problems, the two circles can intersect with each other. The method of cutting in the auxiliary line proves that the method of the proposition allows the students to grasp clearly the known: as shown in Figure 1, ⊙O1 intersects with ⊙O2 and A, B two points, respectively, over A, B two points for a straight line to cross O1.