• Journal for History of Mathematics
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• v.19 no.2
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• pp.101-114
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• 2006

The content and method of geometry taught in secondary school is rooted in 'Elements' by Euclid. On the other hand, however, there are differences between the content and structure of the current textbook and the 'Elements'. The gaps are resulted from attempts to develop the geometry education. Specially, the content and method for the proportional relations of geometric figures has been varied. In this study, we reviewed the changes of the proportional relations of geometric figures with pedagogical point of view. The conclusion that we came to is that the proportional relations in incommensurable case Is omitted in secondary school. Teacher's understanding about the proportional relations of geometric figures is needed for meaningful geometry education.