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Dodecahedral graph : ウィキペディア英語版
Regular dodecahedron

A regular dodecahedron or pentagonal dodecahedron is a dodecahedron that is regular composed of twelve regular pentagonal faces, with three meeting at each vertex, and is represented by the Schläfli symbol . It is one of the five Platonic solids. It has 20 vertices, 30 edges and 160 diagonals (60 face diagonals, 100 space diagonals).〔.〕
==Dimensions==
If the edge length of a regular dodecahedron is ''a'', the radius of a circumscribed sphere (one that touches the regular dodecahedron at all vertices) is
:r_u = a\frac \left(1 + \sqrt\right) \approx 1.401258538 \cdot a
and the radius of an inscribed sphere (tangent to each of the regular dodecahedron's faces) is
:r_i = a\frac \sqrt +\frac\sqrt} \approx 1.113516364 \cdot a
while the midradius, which touches the middle of each edge, is
:r_m = a\frac \left(3 +\sqrt\right) \approx 1.309016994 \cdot a
These quantities may also be expressed as
:r_u = a\, \frac \phi
:r_i = a\, \frac
where ''φ'' is the golden ratio.
Note that, given a regular dodecahedron of edge length one, ''ru'' is the radius of a circumscribing sphere about a cube of edge length ''φ'', and ''ri'' is the apothem of a regular pentagon of edge length ''φ''.

抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)
ウィキペディアで「Regular dodecahedron」の詳細全文を読む



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