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在教学“余弦定理”时,我尽量安排有多种形式的学生练习贯穿在这节课的始终。让学生在练习的过程中复习旧的知识,掌握新的知识,运用新的知识,巩固新的知识。一、复习性练习教师在备课时要深钻教材,把握教材的关键、重点和难点。余弦定理的证法的关键,在于确定任意三角形ABC顶点的坐标。我们在讲授新课前,从复习旧课入手。首先让学生根据三角函数的定义练习这样的题目:如图一,已知∠XOB=A,|OB|=c,求B点的坐标。如果∠A为钝角、直角,B点的坐标又分别如何呢?
In teaching the “cosine theorem”, I try to arrange for many forms of student practice throughout this lesson. Let students review old knowledge, master new knowledge, apply new knowledge and consolidate new knowledge during the practice. First, review the practice of teachers in the preparation of the lesson to drill deep textbooks, grasp the key teaching materials, key and difficult. The key of the cosine theorem is to determine the coordinates of the vertex of an arbitrary triangle ABC. Before we teach a new class, we start by reviewing the old class. First let the students practice the following questions according to the definition of trigonometric functions: As shown in Figure 1, it is known that ∠XOB = A, | OB | = c, find the coordinates of B point. If ∠ A obtuse angle, right angle, B-point coordinates and how?