# integers.info

## Triangle or Trigon

### A polygon with 3 sides

 Interior Angle = 60° Central Angle = 120° Slice Area ≈ 0.433 r2 Total Area ≈ 1.299 r2 Circumference ≈ 5.196 r

A triangle is a polygon with 3 sides, and the sum of its interior angles is 180 degrees. A regular triangle is also called an equilateral triangle.

The values in the table above assume a regular polygon as in the picture. In a regular polygon, all angles and sides are equal, which means that a perfect circle can be drawn across all the vertices. The radius of this circle is called the circumradius, and is denoted r in the calculations above.

The more sides the regular polygon has, the more similar to a circle it becomes. As a result, the circumference gets closer and closer to 2 × π × r (≈ 6.283 r), and the area gets closer and closer to π × r2 (≈ 3.1415 r2).

### List of Polygons

Here are all the polygons with twenty or less sides:

Number of SidesPolygon Name
3Triangle
5Pentagon
6Hexagon
7Heptagon
8Octagon
9Nonagon
10Decagon
11Hendecagon
12Dodecagon
13Tridecagon