Understanding Quadrilaterals Class 8 notes

In this page we will explain the topics for the chapter 3 of Understanding Quadrilaterals Class 8 Maths.We have given good quality Understanding Quadrilaterals Class 8 notes along with video to explain various things so that students can benefits from it and learn maths in a fun and easy manner, Hope you like them and do not forget to like , social share and comment at the end of the page.

Table of Content

What is Closed curve and Open curve

Closed curve is a figure in the plane with no end points. It completely encloses an area
Closed curve
Open curve is a figure in the place with end points
open curve

What are polygons

A simple closed curve made up of only line segments is called a polygon.

Classification of polygons

We classify polygons according to the number of sides( or vertices)
Number of sides

Diagonal in Polygons

A diagonal is a line segment connecting two non-consecutive vertices of a polygon
Diagonal in a Polygon  

Convex and Concave Polygons

Convex Polygon
We have all the diagonals inside the Polygon
Convex Polygon
Concave Polygon
We don’t have all the diagonals inside the Polygon
Concave Polygon
We will be concentrating on Convex Polygon in this chapter

Regular and Irregular Polygons

A regular polygon is both ‘equiangular’ and ‘equilateral’.
So all the sides and angles should be same
(a) So square is a regular polygon but rectangle is not
(b) Equilateral triangle is a regular polygon

Angle Sum in the Polygons

The Sum of the angles in the polygon is given by
=(n-2) × 1800
For Triangle, n=3
So Total =1800
For quadrilateral, n=4
So total =3600
Find the value of angle x
Example on angle sum of quadilaterals
We know in the quadrilateral, sum of interior angle is 3600
Watch this tutorial on how to solve angle problems in quadrilateral

Sum of the Measures of the Exterior Angles of a Polygon

The sum of the measures of the external angles of any polygon is 360°.
This property is very useful is finding number of sides of the polygons

Find the number of sides of a regular polygon whose each exterior angle
has a measure of 60°.
Solution: Total measure of all exterior angles = 360°
Measure of each exterior angle = 60°
Therefore, the number of exterior angles =360/60=6
The polygon has 6 sides.
Watch this tutorial on how to solve exterior angles problems

What is Quadrilaterals

A quadrilateral is a four sides Polygon. It has four angles
Understanding Quadrilaterals
Angle Sum Property
Sum of angles of the Quadrilaterals =3600
Exterior Angle Property
Sum of exterior angles of the Quadrilaterals =3600

Kinds of Quadrilaterals

Kind of Quadrilaterals


Trapezium is a quadrilateral with a pair of parallel sides.
Trapezium a type of quadrilateral

Isosceles trapezium

Trapezium when non-parallel sides of it are of equal length


It is a quadrilaterals having exactly two distinct consecutive pairs of sides of equal length
Here ABCD is a Kite
Kite a type of quadrilateral


It is a quadrilateral whose opposite sides are parallel.
Parallelogram a type of quadrilateral
Here ABCD is a Parallelogram
AD || BC, AB ||CD
Property 1
The opposite sides of a parallelogram are of equal length.
Property 2
The opposite angles of a parallelogram are of equal measure
∠A= ∠C , ∠B= ∠D
Property 3
The adjacent angles in a parallelogram are supplementary.
∠A+ ∠D=180 , ∠B+ ∠C=180
Property 4
The diagonals of a parallelogram bisect each other

Example on Understanding Quadilaterals chapter
Find the value of the angles x,y,z in the parallelograms given above
Angle B and Angle D are opposite angle and are equal
So y=1000
Angle C and Angle B are adjacent angle and are supplementary
So x+100=180
Angle A and Angle C are opposite angle and are equal
So z=800


A rhombus is a quadrilateral with sides of equal length
A rhombus has all the properties of a parallelogram and also that of a kite.
Special Property
The diagonals of a rhombus are perpendicular bisectors of one another


A rectangle is a parallelogram with equal angles
Property 1
Each angle is of 900
Property 2
The diagonals of a rectangle are of equal length


A square is a rectangle with equal sides.
So it has the same property of Rectangle in addition of 4 equal sides
Square :A equal sides quadilateral
The diagonals of a square are perpendicular bisectors of each other.
Watch this tutorial for understanding quadrilaterals


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