• Journal for History of Mathematics
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• v.20 no.3
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• pp.147-166
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• 2007

This study is about the law of cosines. It dealt with its historical origin and the developmental process of the age of Greece, Islam and Modern age. Especially, we tried to find out how the extension of the law of cosines for spherical triangles and tetrahedron from the law of cosines for plane was done. On the basis of this analysis, we investigated how the law of cosines was generated and proved it through the logical demonstration and mathematical induction. This made us find out the mathematical meaning of mathematical concepts.

• Communications of Mathematical Education
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• v.21 no.1 s.29
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• pp.51-64
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• 2007

In this study we generalize the law of cosine(in any triangle the square of one side is equal to the sum of the squares of the other sides minus twice their product times the cosine of their included angle), We find the following generalized law of cosine: in any polygon the square of one side is equal to the sum of the squares of the other sides minus twice their products times the cosines of their included angles, and prove it using vector.