Polygon term originates from the two Greek words "Poly" and "Gon", where "Poly" stands for "many" and "Gon" stands for angle. So the complete word "Polygon" deals with shapes having many angles.
Curves are used to draw a polygon. A polygon is a shape with many sides or angles. It also has edges, vertices and diagonals. Interestingly, the number of angles in a shape is always equal to the number of edges or sides in a polygon. We can visualise and count the angles, edges, vertices and diagonals in a polygon.
What is a curve?
Curve is a plane figure formed by joining a number of points without lifting a pencil from paper and without retracing any portion of drawing.
A curve which does not intersect itself at any point is called an open curve and on the other hand, a curve which intersects itself is called a closed curve.
What is a polygon in geometry?
Polygon is a closed curve which is made up of only finite number of
line segments and any two line segments do not intersect each other except at their end points. It is a two dimensional figure
in geometry.
The line segments of a polygon are called sides or edges and end points of the line segments are called its
vertices or corners.
What are adjacent sides?
Any two sides of a polygon with a common end point are called adjacent sides of the polygon.
What are adjacent vertices?
The end points of a side of a polygon are called adjacent vertices.
Diagonal of a polygon
A diagonal is a line segment which is formed by joining two vertices which are not adjacent.
AC is a diagonal.
BD is a diagonal.
Types of polygon
Convex polygon
A polygon is said to be a convex polygon, if its diagonals completely lie inside of it. Its interior angles are less than 180 degrees.
Concave polygon
A polygon is said to be a concave polygon, if its diagonals completely lie outside of it. Its one or more than one interior angle is more than 180 degrees.
Regular polygon
A regular polygon is a polygon whose all sides and all angles are equal. In other words we can say, it is both equilateral and equiangular.
Interior angle of regular polygon
= (n-2) × 180°
or
= (n-2) × π radian
Square is a regular polygon as its sides are equal and all angles are equal.
Irregular polygon
A polygon which is not a regular polygon, i.e. not an equiangular and equilateral is called irregular polygon.
A rectangle is an irregular polygon.
Simple polygon
It is a flat shape consisting of straight and non intersecting line segments that are joined to form a single
close path. A Simple Polygon does not cross over itself.
It is also called Jordan Polygon.
All convex polygons are simple.
Classification of polygon based on number of sides
| Number of sides of polygon | Name of polygon | Number of angles of polygon |
|---|---|---|
| 3 | Triangle | 3 |
| 4 | Quadrilateral | 4 |
| 5 | Pentagon | 5 |
| 6 | Hexagon | 6 |
| 7 | Heptagon | 7 |
| 8 | Octagon | 8 |
| 9 | Nonagon | 9 |
| 10 | Decagon | 10 |
Frequently Asked Questions
1) What is a polygon?
A closed plane figure formed by line segments and two line segments which intersect at only their end points.
2) What is the sum of the angles of a polygon?
The sum of angles of a polygon with n sides is (n-2)1800.
3) What is the sum of exterior angles of a polygon?
The sum of exterior angles of the polygon is 3600.
4) Is an equilateral triangle a regular polygon?
Yes, an equilateral triangle is a regular polygon as its all sides are equal and all its angles are equal.
5) Is a rectangle a regular polygon also?
No, a rectangle is not a regular polygon as its angles are equal but all sides are not equal.
Solved Examples
1) Find the number of sides of a polygon if each of its interior angles is 1400.
Solution
Let number of sides of polygon = n
Each interior angle =
140 =
140n = 180n - 360
360 = 180n - 140n
360 = 40n
n = 9
2) Find the number of sides of regular polygon if each exterior angle is 400
Solution
Sum of all exterior angle = 3600
Each exterior angle = 400
Number of exterior angles =
Number of exterior angles = 9
∴ Number of sides of polygon = 9
3) If each interior angle of a regular polygon is 1500 then find its exterior angle.
Solution
Each interior angle = 1500.
We know that, interior angles + exterior angles = 1800
1500 + exterior angles = 1800
exterior angles = 1800 - 1500
exterior angles = 300
4) The ratio between exterior angle and interior angle of a regular polygon is 1:5. Find its interior angle.
Solution
Let exterior angle and interior angle be x and 5x respectively.
Also, interior angles + exterior angles = 1800
5x + x = 1800
6x = 1800
x =
x = 300
∴ exterior angle = 300
interior angle = 5x = 5 × 300
i.e. interior angle = 1500
Fill in Blanks Worksheets
| Type: | Blanks |
| Count: | 2 |
- In a regular polygon all sides and all ___________ are equal.
- ___________ triangle is a regular polygon.
- A triangle has no ___________ .
- The sum of exterior angles of a polygon is ___________ .
- Concave polygons have at least one angle more than ___________ .
- The sum of interior angles of a pentagon is ___________ .
- The number of sides of a polygon must be greater than or equal to ___________.
- The sum of interior angles of an eight sided polygon is ___________ .
- A regular hexagon has ___________ diagonals.
- A polygon whose sum of interior angles is 1440° has ___________ sides.
Fill blanks with the number of sides or sum of interior angles of polygon.
| S.N. | Number of sides of polygon | Sum of interior angles of the polygon |
|---|---|---|
| 1) | 12 | ___________ |
| 2) | ___________ | 1620° |
| 3) | 10 | ___________ |
| 4) | ___________ | 1800° |
| 5) | 5 | ___________ |
Write True or False Worksheet
| Type: | True False |
| Count: | 1 |
| S.N. | Statement | ✓ or ✕ |
|---|---|---|
| 1) | A square is a regular polygon. | |
| 2) | A triangle has three diagonals. | |
| 3) | Sum of interior angles of a regular hexagon is 720° | |
| 4) | A n-sided convex polygon has diagonals. | |
| 5) | The right angled triangle is a regular polygon. | |
| 6) | In convex polygons each angle is less than 180°. | |
| 7) | A heptagon has eight sides. | |
| 8) | Each interior angle of a nonagon is 140°. | |
| 9) | The number of sides in a polygon must be a whole number. | |
| 10) | A decagon has 35 diagonals. |
Match Columns Worksheet
| Type: | Matching |
| Count: | 1 |
| Name of polygon | Number of sides of polygon | ||
|---|---|---|---|
| 1) | Pentagon | a) | 7 |
| 2) | Octagon | b) | 9 |
| 3) | Triangle | c) | 10 |
| 4) | Heptagon | d) | 6 |
| 5) | Nonagon | e) | 5 |
| 6) | Decagon | f) | 8 |
| 7) | Hexagon | g) | 3 |
Multiple Choice Questions Worksheet
| Type: | MCQ |
| Count: | 1 |
- hexagon
- decagon
- pentagon
- nonagon
- hexagon
- heptagon
- octagon
- decagon
- = 900
- = 1800
- < 900
- < 1800
- < 900
- < 1800
- > 900
- > 1800
- interior angles are equal
- exterior angles are equal
- sides are equal
- all of these
- 900
- 1800
- 2700
- 3600
- isosceles triangle
- equilateral triangle
- scalene triangle
- rhombus
- 2
- 4
- 1
- 3
- 900°
- 800°
- 700°
- 540°
- 15
- 10
- 11
- 14
