# Decagon

Regular dodecagon

Construction method

Decagon (Nijikaku, Icosagon) is one of, has 20 and 20. The number is 3240 °, and the number of them is 170.

In the regular dodecagon, and is 18 and the interior angle is 162 °. S of a regular dodecagon with a side length of _a _

S = 5 a 2 cot π 20 = 5 (1 + 5 + 5 + 2 5) a 2 ≈ 31.5688 a 2 {\ displaystyle S = 5 a {2} \ cot {\ frac {\ pi} {20}} = 5 \ left (1 + {\ sqrt {5}} + {\ sqrt {5 + 2 {\ sqrt {5}}}} \ right) a ^ {2} \ approx 31.5688 a ^ {2}}! {\ displaystyle S = 5a ^ {2} \ cot {\ frac {\ pi} {20}} = 5 \ left \ (1 + {\ sqrt {5}} + {\ sqrt { 5 + 2 {\ \ sqrt {5}}}} \ right ) a ^ {2} \ approx 31.5688 a ^ {2}}] (https://wikimedia.org/api/rest_v1/media/math / render / svg / 1 db 980571 f 8 cf 35858 2 de 731266 b 603 dd 3 e 77 dab)

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A regular dodecagon is a figure that is possible.

External link

*.. (English) . CS 1 maint: Multiple names: authors list

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Post Date : 2018-02-08 20:30

This article is taken from the Japanese Wikipedia Decagon

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