Octadecagon
A octadecagon or 18-gon is a shape with 18 sides and 18 corners.
Regular octadecagon
All sides of a regular octadecagon are the same length. Each corner is 160°. All corners added together equal 2880°.
Area
The amount of space a regular octadecagon takes up is
The area of a regular octadecagon of side length a is given by
- [math]\displaystyle{ A = \frac{18}{4}a^2\cot\frac{\pi}{18}\simeq 25,5208a^2 }[/math]
Octadecagon Media
Octadecagon with all 135 diagonals
Octadecagon, an exact construction based on the angle trisection 120° by means of the tomahawk, animation 1 min 34 s.
Octadecagon, animation of the approximate construction
Symmetries of a regular octadecagon. Vertices are colored by their symmetry positions. Blue mirrors are drawn through vertices, and purple mirrors are drawn through edge. Gyration orders are given in the center.
en:regular polygon dissection into rhombs, boundary edges have 2 rhombus edges
An equilateral pentagonal dissection, with sequential internal angles: 60°, 160°, 80°, 100°, and 140°. Each of the 24 pentagons can be seen as the union of an equilateral triangle and an 80° rhombus.[1]
9-cube enneract graph
en:Octadecagon dissection into rhombi from 9-cube projection
en:regular polygon dissection into rhombs
18-gon rhombic dissectionx
