Abstract: To study the problem Of the negative influence of "standard figure" in the teaching of plane geometry, the author set up 3 experimental classes. In one class oral explanation was used, in the second the variant figures were used, in order to generalize the "standard figure", and the third in class used standard figure from textbooks. The results of the experiment confirm: (1) in learning fundamental" concepts, the negative influence of the "standard figure" was quite" serious, but later the influence is limited in prolonging the time in prceiving variant figure and in increasing the frequencies of trial and error; (2) when variant figureand oral explanation were used in different classes of 14—15-year old pupils, similar results were obtained. Therefore, oral explanation should be used to generalize the standard figure as earlier as possible.

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