Icosagon facts for kids

An icosagon is a cool shape that has 20 straight sides and 20 corners. Imagine a shape with lots and lots of sides! Inside, each corner of a regular icosagon measures 162 degrees. The angles on the outside are 198 degrees.

What is a Regular Icosagon?

A regular icosagon is special because all its 20 sides are the same length. Also, all its 20 corners are exactly the same. You can make a regular icosagon by "cutting off" the corners of a decagon (a 10-sided shape). You can even make it by cutting the corners of a pentagon (a 5-sided shape) twice!

How to Find the Area

The area is the amount of space a shape covers. For a regular icosagon, you can find its area using this formula:

Here, a stands for the length of one of its sides.

Fun Uses of the Icosagon

Icosagons might seem like just a math shape, but they show up in some interesting places!

• The Big Wheel on the popular US game show The Price Is Right has a cross-section shaped like an icosagon.
• The famous Globe Theater, where William Shakespeare's plays were performed, was built on an icosagonal (20-sided) foundation. This was discovered when parts of it were dug up in 1989.
• Some golygon paths, like the swastika symbol, can be thought of as an irregular icosagon.

A regular square, pentagon, and icosagon can fit perfectly together around a point.

Taking Apart an Icosagon

Imagine you have a regular icosagon. You can actually cut it into smaller shapes! A mathematician named Coxeter found that a 20-sided shape (where m=10) can be cut into 45 smaller shapes called rhombs. A rhomb is like a squished square. For an icosagon, these 45 shapes include 5 squares and 4 sets of 10 rhombs.

Dissection into 45 rhombs

Images for kids

• 

  Icosagon with a given side length, shown in an animation.

• 

  This image shows the different ways a regular icosagon can be symmetrical.

See also

In Spanish: Isodecágono para niños