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Dodecagon (12-gon)
From Greek duo "two" + deka "ten" + gonia "angle"
Definition: A polygon with 12 sides
Try this
Adjust the dodecagon below by dragging any orange dot. By clicking on the top left command line,
you can switch it between a
regular and
irregular dodecagon.
(If there is no image below, see support page.)
Properties of regular dodecagons
| Interior angle |
150° |
Like any regular polygon, to find the interior angle we use the formula
(180n–360)/n . For a dodecagon, n=12.
See Interior Angles of a Polygon |
| Exterior Angle |
30° |
To find the exterior angle of a regular dodecagon, we use the fact that the exterior angle
forms a
linear pair
with the interior angle, so in general it is given by the formula
180-interior angle.
See Exterior Angles of a Polygon |
| Area |
11.196s2
approx
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Where S is the length of a side.
To find the exact area of a dodecagon or any polygon, using various methods,
see Area of a Regular Polygon and
Area of an Irregular Polygon |
Properties of all dodecagons
| Number of diagonals |
54 |
The number of distinct diagonals possible from all vertices. (In general ½n(n–3) ).
In the figure above, click on "show diagonals" to see them.
See Diagonals of a Polygon |
| Number of triangles |
10 |
The number of triangles created by drawing the diagonals from a given vertex. (In general n–2).
In the figure above, click on "show triangles" to see them. See Triangles of a Polygon |
| Sum of interior angles |
1800° |
In general 180(n–2) degrees .
See Interior Angles of a Polygon |
Dodecagonal coins
Dodecagons are not seen much in everyday life. However, in Australia, there are coins in the shape of a dodecagon.
Below is the 12-sided Australian 50 cent coin.
Related polygon topics
General
Types of polygon
Area of various polygon types
Perimeter of various polygon types
Angles associated with polygons
Named polygons
(C) 2008 Copyright John Page
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