

Heptagon (7gon)
From Greek hepta "seven" + gonia "angle"
Definition: A polygon with 7 sides
also: Septagon
Try this
Adjust the heptagon below by dragging any orange dot. By clicking on the top left command line,
you can switch it between a
regular and
irregular heptagon.
Properties of regular heptagons
Interior angle 
128.571° 
Like any regular polygon, to find the interior angle we use the formula
(180n–360)/n . For a heptagon, n=7.
See Interior Angles of a Polygon 
Exterior Angle 
51.429° 
To find the exterior angle of a regular heptagon, 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 
3.633s^{2} approx

Where S is the length of a side.
To find the exact area of a heptagon or any polygon, using various methods,
see Area of a Regular Polygon and
Area of an Irregular Polygon 
Properties of all heptagons
Number of diagonals 
14 
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 
5 
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 
900° 
In general 180(n–2) degrees .
See Interior Angles of a Polygon 
Heptagonal coins
Heptagons are not seen much in everyday life except in the UK, where there are coins in the shape of a heptagon.
On the right is the 50 pence coin. It is not a strict heptagon because the sides are actually curved arcs instead of straight lines.
The resulting shape is known as an "Equilateral Curve Heptagon".
It has one very curious property; in spite of not being a circle it has the same diameter everywhere!
This is done so that it will always fit
in coinoperated machines, but still feel different in the hand from
other round coins  a help to sightimpaired people.
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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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