integers.info

Polygons

Triangle or Trigon

A polygon with 3 sides

Interior Angle=60°
Central Angle=120°
Slice Area0.433 r2
Total Area1.299 r2
Circumference5.196 r

About Triangles

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.

About Regular Polygons

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
4Quadrilateral
5Pentagon
6Hexagon
7Heptagon
8Octagon
9Nonagon
10Decagon
11Hendecagon
12Dodecagon
13Tridecagon
14Tetradecagon
15Pentadecagon
16Hexadecagon
17Heptadecagon
18Octadecagon
19Enneadecagon
20Icosagon