- 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.
When the stock market crashed, Franklin D. Roosevelt got on the television and didn’t just talk about the, you know, the princes of greed. He said, ‘Look, here’s what happened.’
Joe Biden, Interview with CBS Evening News