Polygons – Classification

We classify polygons to the number of side or
vertices based they have.

A polygon can be classified by it’s number of a sides and measure of angles.

First, we classify by it’s number of a sides. 

             Classified by measuring the sides

The name of a polygon usually depends on how many sides or lines the shape has.

Any shape that can be drawn by three connecting straight lines is a triangle, shape that can be drawn by four connecting straight lines is a quadrilateral, and shape that can be drawn by five connecting straight lines is a pentagon.

if a polygon has three sides it’s called triangle, if it has four sides it’s called quadrilateral,if it has five sides it’s called pentagon.

Note: A circle is not a polygon because it is formed with curved line, if any curved line is used to form a close figure than it will not be a polygon.

There are some names of polygons that usually occur in everyday.

Sides                 Polygon 

3                    Triangle 

4                     quadrilateral 

5                     pentagon

6                     hexagon

 7                     heptagon

8                     octagon

 9                     nonagon

10                    decagon

12                    dodecagon

n sides              n-gon 

When a polygon has 300 sides it will be known as 300-gon. 

Triangle: A three sided polygon is known as the triangle.

Quadrilateral: A four sided polygon is known as the quadrilateral.

Pentagon: The five sided polygon is known as the pentagon.

Hexagon: The closed figure which is formed by six straight lines is known as hexagon.

Heptagon: A polygon which has seven sides is known as heptagon.

Octagon: A closed figure which is made by eight straight lines is known as octagon.

Nonagon: As the name says, the nine sided polygon is known as  nonagon.

Decagon: The closed figure which is formed by ten straight lines is known as decagon.

1. Triangle:

a.   Number of sides or vertices = 3
b.   Figure

2. Quadrilateral:

a.   Number of sides or vertices = 4
b.   Figure

3. Pentagon:

a.   Number of sides or vertices = 5
b.   Figure

4. Hexagon:

a.   Number of sides or vertices = 6
b.   Figure

5. Heptagon:

a.   Number of sides or vertices = 7
b.   Figure

6. Octagon:

a.   Number of sides or vertices = 8
b.   Figure

7. Decagon:

a.   Number of sides or vertices = 10
b.   Figure

8. Dodecagon:

a.   Number of sides or vertices = 12

b.   Figure

             Classified by measuring the angles

                          Regular polygon

A polygon which has all sides are congruent(equal) and all angles are congruent (equal) is known as a regular polygon.

If a triangle has all the sides are same and all the angles are same then it is a equilateral triangle or a regular triangle.

If a quadrilateral has all the sides are same and all the angles are same then it is a square or a regular quadrilateral..

Irregular polygon
A polygon which has all sides are not congruent(not equal) or different in length and all angles are not congruent (not equal) or different in measure the polygon is known as a irregular polygon.

Above all of shapes are polygons. We notice that all the shapes are drawn with only straight lines and all the sides are connect. 
 Not a polygon

In above shapes we notice that one shape is curved and other shape all the straight lines are not fully connected, so it can’t be called a polygon.