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Derivation of the law of cosines via the incircle. (English)
Forum Geom. 13, 133-134 (2013).
In this article the authors derive the famous law of cosines without using special cases and without using the Pythagorean theorem deriving a formula by equating independent expressions for the radius $r$ of the incircle of the given triangle.
Reviewer: Francisco Vittone (Rosario)
Classification: G60
Keywords: law of cosines
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