In geometry

Geometry

Geometry arose as the field of knowledge dealing with spatial relationships. Geometry was one of the two fields of pre-modern mathematics, the other being the study of numbers ....

, an icosagon is a twenty-sided polygon

Polygon

In geometry a polygon is a flat shape consisting of straight lines that are joined to form a closed chain orcircuit.A polygon is traditionally a plane figure that is bounded by a closed path, composed of a finite sequence of straight line segments...

. The sum of any icosagon's interior angles is 3240 degrees.

One interior angle in a regular

Regular polygon

A regular polygon is a polygon that is equiangular and equilateral . Regular polygons may be convex or star.-General properties:...

 icosagon is 162° meaning that one exterior angle would be 18°

The regular icosagon is a constructible polygon

Constructible polygon

In mathematics, a constructible polygon is a regular polygon that can be constructed with compass and straightedge. For example, a regular pentagon is constructible with compass and straightedge while a regular heptagon is not....

, by an edge-bisection

Bisection

In geometry, bisection is the division of something into two equal or congruent parts, usually by a line, which is then called a bisector. The most often considered types of bisectors are the segment bisector and the angle bisector In geometry, bisection is the division of something into two equal...

 of a regular decagon

Decagon

In geometry, a decagon is any polygon with ten sides and ten angles, and usually refers to a regular decagon, having all sides of equal length and each internal angle equal to 144°...

, and can be seen as a truncated

Truncation (geometry)

In geometry, a truncation is an operation in any dimension that cuts polytope vertices, creating a new facet in place of each vertex.- Uniform truncation :...

 decagon.
One of the most famous uses of an icosagon is the Showcase Showdown wheel on the popular US game show The Price Is Right

The Price Is Right (US game show)

The Price Is Right is an American game show which was created by Mark Goodson and Bill Todman. Contestants compete to identify the pricing of merchandise to win cash and prizes. The show is well-known for its signature line of "Come on down!" when the announcer directs newly selected contestants to...

.

The Globe, the outdoor theater used by William Shakespeare's acting company, was discovered to have been built on an icosagonal foundation when a partial excavation was done in 1989.