Definition:Icosahedron
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Definition
An icosahedron is a polyhedron which has $20$ faces.
Regular Icosahedron
A regular icosahedron is an icosahedron whose $20$ faces are all congruent equilateral triangles.
Truncated Icosahedron
A truncated icosahedron is an icosahedron whose $12$ vertices are truncated such that one third of each edge is cut off at each of both ends.
Also see
- Results about icosahedra can be found here.
Linguistic Note
The word icosahedron derives from the Classical Greek εἰκοσάεδρον:
- eíkosi (εἴκοσι), meaning twenty
- hedron (a form of ἕδρα), meaning base or seat.
The technically correct plural of icosahedron is icosahedra, but the word icosahedrons can often be found.
Sources
- 1986: David Wells: Curious and Interesting Numbers ... (previous) ... (next): $20$
- 1989: Ephraim J. Borowski and Jonathan M. Borwein: Dictionary of Mathematics ... (previous) ... (next): icosahedron
- 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $20$
- 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): icosahedron (plural icosahedra)
- 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): icosahedron (plural icosahedra)
- 2014: Christopher Clapham and James Nicholson: The Concise Oxford Dictionary of Mathematics (5th ed.) ... (previous) ... (next): icosahedron (icosahedra)