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Pythagoras extended: A geometric approach to the cosine rule

Published online by Cambridge University Press:  01 August 2016

Neil Bibby
Affiliation:
32 Guildford Road, Brighton BN1 3LW
Doug French
Affiliation:
Department of Educational Studies, University of Hull, 173 Cottingham Road, Hull HU5 2EH

Extract

The motivation for this article was the desire to make the cosine rule in some way geometrically “obvious”. What we have ended up with is a mixture of inductive and deductive approaches which we hope goes some way to illuminating the cosine rule, and to enhancing students' relational understanding of it. The germ of these ideas can be sown soon after students have met Pythagoras, with the question “O.K., suppose the triangle ABC is not rightangled: what can we say about a2, b2 and c2 now?”

Type
Research Article
Copyright
Copyright © The Mathematical Association 1988

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