Triangles

problem

Impossible Triangles?

Age

16 to 18

Challenge level

Which of these triangular jigsaws are impossible to finish?
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Incircles Explained

This article is about triangles in which the lengths of the sides and the radii of the inscribed circles are all whole numbers.
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Interacting With the Geometry of the Circle

Jennifer Piggott and Charlie Gilderdale describe a free interactive circular geoboard environment that can lead learners to pose mathematical questions.
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Making Maths: Equilateral Triangle Folding

Make an equilateral triangle by folding paper and use it to make patterns of your own.
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Making Maths: Test the Strength of a Triangle

Have you noticed that triangles are used in manmade structures? Perhaps there is a good reason for this? 'Test a Triangle' and see how rigid triangles are.
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Peg and Pin Boards

This article for teachers suggests activities based on pegboards, from pattern generation to finding all possible triangles, for example.
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Liethagoras' Theorem

Liethagoras, Pythagoras' cousin (!), was jealous of Pythagoras and came up with his own theorem. Read this article to find out why other mathematicians laughed at him.
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Squareo'scope Determines the Kind of Triangle

A description of some experiments in which you can make discoveries about triangles.