A plane figure bounded by straight lines is called a rectilinear figure and any closed rectilinear figure is called a polygon.

### Types of polygons

**Equiangular Polygons:** If all the angles of a polygon are equal, then it is called an equiangular polygon.

**Equilateral polygon: **If all the sides if a polygon are equal, then it is called an equilateral polygon.

Note: Except for triangles, an equilateral polygon need not necessarily be an equiangular polygon and vice versa.**Regular Polygon: **If all the sides and all the angles of a polygon are equal, then it is called a regular polygon.

Here, ABCDEF is a regular polygon.

AB = BC = CD = DE = EF = FA and also all the interior angles are equal.**Convex polygon: **

If all the interior angles of a polygon are less than 180^{o}, then it is called a convex polygon.**Concave polygon:**If one or more of the interior angles of a polygon are reflex angles, i.e. greater than 180

^{o}, then it is called a concave polygon.

Names of polygons based on the number of sides:

3 - Triangle

4 - Quadrilateral

5 - Pentagon

6 - Hexagon

7 - Septagon or Heptagon

8 - Octagon

9 - Nonagon

10 - Decagon

### Properties of polygons

1. A diagonal of a polygon is the straight line which joins any two non-adjacent vertices of the polygon.

2. An exterior angle is obtained when any one side of a polygon is extended or produced.

3. Unless otherwise stated a polygon typically means a convex polygon.

4. In a polygon of n sides, the sum of interior angles is equal to (n - 2) x 180^{o}.

5. In a polygon of n sides, the sum of exterior angles is equal to 360^{o}.

6. At each vertex of a polygon, exterior angle + interior angle = 180^{o}.

7. Area of a regular hexagon = 6 times the area of an equilateral triangle with the length of the side same as that of the regular hexagon.