

Decagon (10gon)
From Greek deka "ten" + gonia "angle"
Definition: A polygon with 10 sides
Try this
Adjust the decagon below by dragging any orange dot. By clicking on the top left command line,
you can switch it between a
regular and
irregular decagon.
Properties of regular decagons
Interior angle 
144° 
Like any regular polygon, to find the interior angle we use the formula
(180n–360)/n . For a decagon, n=10.
See Interior Angles of a Polygon 
Exterior Angle 
36° 
To find the exterior angle of a regular decagon, 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
180interior angle.
See Exterior Angles of a Polygon 
Area 
7.694s^{2} approx

Where S is the length of a side.
To find the exact area of a decagon or any polygon, using various methods,
see Area of a Regular Polygon and
Area of an Irregular Polygon 
Properties of all decagons
Number of diagonals 
35 
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 
8 
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 
1440° 
In general 180(n–2) degrees .
See Interior Angles of a Polygon 
Other polygon topics
General
Types of polygon
Area of various polygon types
Perimeter of various polygon types
Angles associated with polygons
Named polygons
(C) 2011 Copyright Math Open Reference. All rights reserved

