Table of Contents
16 December 2020
Read time: 5 minutes
Geometry is a branch of maths that deals with the study of various different shapes and their properties. When line segments join together to form a closed circuit then they are called "POLYGONS". Here we will study the properties of a few polygons.
What are Polygons?
A closed GEOMETRICAL figure having a definite number of line segments connected together are called "POLYGONS"
Polygons can be broadly classified into four types depending on their shapes, they are:
 Regular polygons
 Irregular polygons
 Concave polygons
 Convex polygons
What are Polygons?  PDF
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📥  What are Polygons?  PDF 
Classification of Polygons
Types of polygons  Definition  Examples 

Regular polygons  These are Polygons having the same length on all sides and having equal interior angles.  
Irregular polygons  These Polygons do not have the same length on all sides and their interior angles also differ from each other.  
Concave polygons  If a polygon has one or more interior angles greater than 180 degrees then it is a concave polygon.  
Convex polygon  These type of polygons have all their interior angle less than 180 degrees. 
Different Types of Polygon
Type of Polygon  Sides  Shape  Angles 

Triangle  3  60^{o}  
Square  4  90^{o}  
Pentagon  5  108^{o}  
Hexagon  6  120^{o}  
Heptagon  7  128.5^{o}  
Octagon  8  135^{o}  
Nonagon  9  140^{o}  
Decagon  10  144^{o} 
Is a circle a polygon?
No, circles are not polygons. A polygon is one that has a line segment connected to form a closed figure. But in the case of a circle, its sides intersect at any place other than at the end of its sides.
"The path that surrounds the area".
Example 1 
Perimeter of above figure= 10+5+10+5=30 units.
In general, the Perimeter (P) of any polygon can be formulated by
P=n x l 
The area of a polygon is the surface surrounded by a perimeter.
Area of the above figure, A=l x b (since it is a rectangle)
A=10 × 5 = 50 square units
Let's discuss in detail how to formulate the area and perimeter of the triangle, pentagon, and Hexagon?
Area and perimeter of triangles
A triangle is a polygon having 3 sides and their interior angles summing up to 180°. Triangles can be classified into three types based on their sides and three types based on their angles.
The perimeter of a triangle = 3l
where l= length of sides
3= number of sides of the polygon
Types of Triangles

Based on the sides
Scalene Triangle 
Lengths of all the sides of a triangle are not equal and their angles are different. 

Isosceles Triangle 
Any two side lengths and angles of a triangle are equal. 

Equilateral Triangle 
The length of all three sides and angles are equal. 

Based on angle{interior angles} measurement
Acute angled Triangle 
Angles measuring less than 90°. 

Obtuse angled Triangle 
One of its angle measure more than 90°. 

Rightangled Triangle 
One of its angles measures 90° and the remaining two measures 45°. 
Area of a triangle
In general, the area of a triangle is defined as "half a time product of its base and height".
A=½ x b x h 
Formula to find Area of Equilateral Triangle
Formula to find the area of rightangled Triangle
Area (A) =½ (b × c) 
Heron's Formula
where a, b, c are sides of the triangle s=semi perimeter 
Example 2 
The sides of a triangular park are in the ratio 12:17:25 and its perimeter is 1080 m. What is its area?
Solution:
The sides of the triangle are 12x, 17x, and 25x.
Thus, the sides of the triangle are 240 m, 340 m, and 500m.
Now, the semiperimeter of the triangle is, s=1080/2=540 m.
the area of the triangle is:
Area and perimeter of a Pentagon
Pentagon is a polygon having five sides and again Pentagon's may be regular, irregular, concave, and convex depending on sides. But, a regular pentagon has five sides of equal length and interior angle measuring 108° and an exterior angle of 72°.
Where s: side length of pentagon a: apothem length 
The line segment drawn from the Centre of the pentagon to an is the side of the pentagon is called as "APOTHEM". It is calculated using the length of one side and the measure of the interior angle.
If only the side length of the pentagon is given:
Perimeter of pentagon (P) \( =5 × s\) Where s =side length of pentagon. 
Example 3 
Find the area and perimeter of a regular pentagon whose side is 7 cm and apothem length is 8 cm.
Solution:
Given: The side of a pentagon, a= 7cm
Area = 280 sq.cm 
Perimeter of a pentagon,
P = 5a units
P = 5(5)
P = 25 cm
Perimeter = 25 cm. 
Area and perimeter of Hexagon
A hexagon is a polygon having 6 sides and when divided into a triangle they form 6 Equilateral triangles it has an interior angle of 120° and an exterior angle of 60°.
Perimeter P = 6 x s Where, s = side length of Hexagon. 
Example 4 
If the area of the hexagon is 25 sq.cm. Find its perimeter.
Solution:
Given, Area A = 25 sq.cm
Therefore the side length of the hexagon is 3.1 cm.
Perimeter=number of sides×side length
Summary
From the above topic, we clearly understood the properties of a few polygons and how to formulate their area and perimeter. A closed geometrical figure having a definite number of line segments connected together are called Polygons. They are of different types and have different angles and properties.
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Frequently Asked Questions (FAQs) on Polygons
How many sides does a pentagon have?
A Pentagon is a 5 sided polygon.
How to find the area of a hexagon?
The Area of a Hexagon can be expressed as 6 times the area of an equilateral triangle, which is written as \(\frac{3\sqrt{3}}{2}\times a^2\)
How many sides does a hexagon have?
A Hexagon has 6 sides.
How many diagonals does a hexagon have?
A Hexagon has 9 diagonals.
External References
Written by Nethravathi C, Cuemath Teacher