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初中几何第二册“5.20点的轨迹”一节,是平面几何教学中的一大难点。我采用如下教法,化难为易,效果较好。一、列举反例,深化对轨迹的纯粹性和完备性的认识教本指出:“一般地,如果下面的两个命题,都是正确的,即1.图形 F 上的每一个点,都符合某个条件 C;2.符合某个条件 C 的每一个点,都在图形上,那么我们说,符合某个条件 C 的点的轨迹是图形 F。
The second chapter “5.20 point trajectory” of junior high school geometry is a major difficulty in the teaching of plane geometry. I use the following teaching methods to make it easier and more effective. First, enumerating counterexamples and deepening the understanding of the pureness and completeness of the trajectory: "Generally speaking, if the following two propositions are all correct, that is, 1. Each point on the graph F matches a certain point. Condition C; 2. Each point that meets a certain condition C is on the graph, then we say that the trajectory of the point that meets a condition C is graph F.