Ode to Equilateralism

Published by patrick honner on

Equilateral 1Today, 10/10/10, is Equilateral Triangle Day!  This day doesn’t come around that often, so I thought I’d expound a bit on the virtues of equilateralism.

There is so much to appreciate about the equilateral triangle–its uniform shape, its simple area formula, its presence in regular hexagons, its decomposition into 30-60-90 triangles–and most of these properties are a consequence of the equilateral triangle’s abundance of symmtery.

Consider this plain old non-equilateral triangle.

plain triangle

In any triangle, from any vertex there are three important segments you can draw–the angle bisector, the altitude, and the median.  Each of the segments defines a kind of symmetry for that part of the triangle.


Notice how these three segments are all quite different in our plain old non-equilateral triangle.  But, if we were to make the two sides from that vertex the same length (i.e., make the triangle isosceles), all those segments become equal!

Isosceles Triangle

The sides being the same length force all those lines of symmetry to become one.  Now, the beauty of the equilateral triangle is that it’s like three isosceles triangles rolled into one! 

Equilateral 2

It’s an isosceles triangle from every vertex!  So, all those lines of symmetry are the same no matter how you look at it.

Enjoy the next 397 days, until the next Equilateral Triangle Day.

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Categories: Geometry

patrick honner

Math teacher in Brooklyn, New York

1 Comment

Alan · October 10, 2010 at 1:00 pm

There won’t be a 13/13/13. T.T

Anyway, Equilateral Triangle Day is an important holiday. How else would TV networks stay in business without their respective Halloween marathons, soon to be Thanksgiving marathons next year, and Christmas the next. And maybe the fact that there won’t be one in 2013 supports the 2012 theory. O.O

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