What is the difference between a polyhedron and a regular polyhedron?

Answer 1

A Polyhedron is a closed plane figure whose faces are portions of planes. Prisms and pyramids are examples of Polyhedron's. While a Regular Polyhedron is a Polyhedron whose facces are all regular Polygons and whose Vertices are all alike. There are only five Regular Polyhedron's: Tetahedron , Octahedron , Icosahedron , Hexahedron , and Dodecahedron .

To clarify, there are five known Platonic Solids: regular polyhedrons which are convex on all their vertices.

The tetrahedron is also known as the triangular pyramid: a regular one has an identical equilateral triangle for each of its four faces. This is the one Platonic solid which is self-dual, as each face has three sides and each vertex joins three edges.

The regular hexahedron is better known as the cube: each of its six faces is a square, and each vertex joins three edges. Its dual counterpart is the regular octahedron. In this case, each of its eight faces is three-sides (an equilateral triangle) and each vertex joins four edges. To picture the octahedron, think two square pyramids mated on their square faces, leaving only the triangular faces.

Finally, there is the regular dodecahedron (12 faces), which is composed of regular pentagons (five sides). Each vertex again joins three edges. Its dual counterpart is the regular icosahedron. It has 20 triangular faces, and each vertex joins five edges.