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3D Generalisations of Viviani's theorem

Published online by Cambridge University Press:  23 January 2015

Michael De Villiers*
Affiliation:
Dept. of Mathematics & Computer Science Education, University of KwaZulu-Natal, South Africa e-mail: profmd@mweb.co.za

Extract

“The ambitious learner should carefully study a new fact; he should turn it over and over, consider it under various aspects, scrutinize it from all sides … Moreover, he should try to expand and enlarge any newly acquired knowledge by application, generalization, specialization, analogy, and in all other ways.” [1]

Vincenzo Viviani, a 17th century mathematician, proved that the sum of the (perpendicular) distances from a point within an equilateral triangle to its sides is constant as shown in Figure 1. The theorem, named after him, generalises to polygons that are equilateral or equi-angled, or to 2n-gons with opposite sides parallel. Viviani's theorem is easily proved by summing the areas of triangles APB, BPC and CPA, equating to the area of the triangle ABC, and then simplifying to obtain h1 + h2 + h3 = H, where H is the altitude of ABC.

Type
Articles
Copyright
Copyright © The Mathematical Association 2013

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