A tetrahedron is its own dual.
An octahedron is the dual of a cube and conversely.
An icosahedron is the dual of a dodecahedron and conversely.
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Platonic solids are 3D shapes formed using only regular shapes. Only 1 type of regular shape is used to make a platonic solid. Platonic solids are the simplest and purest form of 3D shapes.
There are 5 platonic solids which are the only 5 regular polyhedra (possible).Plato attributed 4 of them to the 4 elements:Fire ≡ TetrahedronEarth ≡ CubeAir ≡ OctahedronWater ≡ IcosahedronAristotle added the fifth element "Ether" saying the heavens were made of it; he did not associate the fifth platonic solid, the Dodecahedron, to it.
Answering your questions one at a time.1 - What is a platonic solid?A platonic solid is one with all faces congruent polygons, meaning that they all have the same number of sides, vertices and angle size.2 - How many are there?There are only and exactly five.3 - What are their names?TetrahedronCube (but when talking about Platonic solids, it is commonly referred to as a "hexahedron").OctahedronDodecahedronIcosahedronNote: These individual platonic solids can be identified by their unique Schlafli Symbol. This is demonstrated through the following:{p,q}p = Number of vertices at each faceq = Number of faces at each vertexSo for a dodecahedron, the Shlafli Symbol would be {5,3}, because a pentagon has five {5, or p} vertices, and at any individual vertex three {3, or q} faces meet.Understand? Great!
tetrahedron
A Platonic solid is a regular, convex polyhedron. The same amount of edges must meet at each vertex, all the faces need to be uniform, and all the dihedral angles must be the same.