在已经学习了圆的对称性后,学生对弧、弦、圆心角,垂径定理等已有了一定的了解。接下来讲解圆周角的定义及性质。在证明同弧所对的圆周角是圆心角的一半这一性质中,直径起着举足轻重的作用,是一个不可替代的因素。如何利用好直径这个条件,对学生在圆周角性质的证明方法的归纳时更有帮助?下面就这些问题简单地探讨一下。一、直径这条辅助线,应直接给出比较好学生本节课的重要目标之一就是能理解同弧所对的圆周角 After having learned the symmetry of the circle, students have some knowledge of the arcs, chords, central angles, and the theorem of the diameter of the beads. Next, explain the definition and nature of the circumferential angle. Diameter plays a decisive role in proving that the circumferential angle to the arc is half of the central angle is an irreplaceable factor. How to make good use of the condition of diameter is more helpful for the students to summarize the method of proving the nature of the circumferential angle. The following is a brief discussion of these problems. First, the diameter of the auxiliary line should be given directly to better students One of the important goals of this lesson is to understand the same angle with the arc