Meet the Platonic Solids: Tetrahedron
The Platonic solids have been known since antiquity, and they
play a prominent role in Plato's description of the physical world.
The planar faces of each solid are identical polygons. Only
equilateral triangles, squares and regular pentagons appear.
Although the platonic solids seem to be purely geometric
objects, they embody a number of deep algebraic features. Their
symmetries, for example, relate to the solution of polynomial
equations of low degree.
If you would like to learn more about Platonic solids, you can
start here.