

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
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