Believe, when you are most unhappy, that there is something for you to do in the world. So long as you can sweeten another’s pain, life is not in vain.
Helen Keller, We Bereaved (1929)
- Regular tetrahedron (Wikipedia)
A regular tetrahedron is a tetrahedron in which all four faces are equilateral triangles. In other words, all of its faces are the same size and shape (congruent) and all edges are the same length. A convex polyhedron in which all of its faces are equilateral triangles is the deltahedron. There are eight convex deltahedra, one of which is the regular tetrahedron.
