Images for Mathematics

The regular polyhedra are five

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A way to see why there are only 5 regular polyhedra: we can use equilateral triangles as faces of a polyhedron by putting 3 or 4 triangles around each vertex (as we can see in the picture: in this case we get the octahedron), otherwise we can put also 5 triangles.
The image has been realized for the exhibition Simmetria, giochi di specchi - Symmetry, playing with mirrors.

The image belongs to the sections...:
All together (3D geometry)