The ancient Greek mathematician Euclid proved in his Elements of Geometry that there are only five Platonic solids – the regular tetrahedron (four sides that are equilateral triangles), the cube (six ...

STEP 3: Three regular triangles on a corner make a tetrahedron, four make an octahedron ... So only three Platonic solids can be made from triangles. Image caption, Three squares make the corner ...