【教材分析】1、作为《圆》这章的第一个重要性质,它研究的是垂直于弦的直径和弦的关系。2、该性质是圆的轴对称性的演绎,也是今后证明圆中线段相等、角相等、弧相等、垂直关系的重要依据,同时为后面圆的计算和作图提供了方法和依据。【教学目标】1.知识目标:①通过观察实验,使学生理解圆的轴对称性;②掌握垂径定理,理解其证明,并会用它解决有关的证明与计算问题;③掌握辅助线的作法--过圆心作一条与弦垂 [Textbook analysis] 1, as the first important feature of the “circle” chapter, it is studied perpendicular to the chord diameter and chord relationship. 2. This property is a deduction of circular axis symmetry. It is also an important basis for proving the equilateral, equilateral, arc-equal and vertical relationship of the line segments in the future, and provides the method and basis for the calculation and mapping of the following circles. [Teaching Objectives] 1. Knowledge goals: ① by observing the experiment, so that students understand the circular axis symmetry; ② grasp the vertical theorem, understand the proof, and will use it to solve the problem of proof and calculation; ③ grasp the auxiliary line Practice - around the center of a chord hanging