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## 'Triangles to Tetrahedra' printed from http://nrich.maths.org/

What is a tetrahedron? Here are four different triangles made
from Polydron (plastic shapes which click together):

Small equilateral

Isosceles

Right angled isosceles

Large equilateral

The sides of the small equilateral triangle are the same length as
the short side of the isosceles triangle and the short sides of the
right-angled isosceles triangle.

The sides of the large equilateral triangle are the same length
as the long sides of the isosceles triangle and the long side of
the right-angled isosceles triangle.

You have an unlimited number of each type of triangle.

How many different tetrahedra can you make? Convince us you have
found them all.

Images reproduced with kind permission from Polydron International Limited .