## pentagons

Noun

- plural form of
*pentagon*

- The names of these five solids are: (r) the tetrahedron, enclosed by four equilateral triangles; (2) the cube or hexahedron, enclosed by 6 squares; (3) the octahedron, enclosed by 8 equilateral triangles; (4) the dodecahedron, enclosed by 12
**pentagons**; (5) the icosahedron, enclosed by 20 equilateral triangles. - Three
**pentagons**may be placed at a common vertex to form a solid angle, and by forming several such sets and placing them in juxtaposition .a solid is obtained having 12 pentagonal faces, 30 edges, and 20 vertices. - The
**pentagons**belong to a dodecahedron, and 20 triangles to an icosahedron; the remaining 60 triangles belong to no regular solid. - In crystallography, the regular or ordinary dodecahedron is an impossible form since the faces cut the axes in irrational ratios; the "pentagonal dodecahedron" of crystallographers has irregular
**pentagons**for faces, while the geometrical solid, on the other hand, has regular ones.

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