In this chapter we will about the concept of regular and irregular quadrilaterals with properties and examples.

## What are regular Quadrilaterals ?

The quadrilaterals in which all sides and angles are of equal measurement are called regular quadrilaterals.

Given above is the square ABCD in which all sides measure a cm and all angles measure 90 degrees.

Area of square is calculated using following formula;

Area of Square = Side x Side

Area of Square = a . a = \mathtt{a^{2}}

The quadrilaterals which have different side and angle measurement are called irregular quadrilaterals.

Some common examples of irregular quadrilaterals are;

### (a) Rectangle

In rectangle opposite sides are of equal measurement and all angle measure 90 degree.

In the above rectangle ABCD;
⟹ Length is a cm

Area of Rectangle is calculated using following formula;

Area of rectangle = Length x Breadth

Area of rectangle = \mathtt{ab\ cm^{2}}

### (b) Parallelogram

In parallelogram opposite sides and angles are equal.

Given above is the parallelogram ABCD in which;

Opposite sides are equal
AB = CD = a cm

Opposite angles are equal
∠A = ∠C
∠B = ∠D

Area of Parallelogram is calculated using following formula;

Area of parallelogram = base x height

Area of parallelogram = \mathtt{ah\ cm^{2}}

### (c) Rhombus

Rhombus is a quadrilateral in which all sides are equal and opposite angles are equal.

Given above is the Rhombus ABCD in which;

All sides are equal
AB = BC = CD= DA = a cm

Opposite angles are equal
∠A = ∠C
∠B = ∠D

Area of Rhombus is calculated using following formula;

Area of Rhombus = 1/2 x product of two diagonals

Area of Rhombus = 1/2 x (d1) x (d2)

(d) Trapezium

Trapezium is a quadrilateral in which contain two parallel sides and two non parallel sides.

In trapezium, both sides and angles are of different measure.

Given above is the trapezium ABCD in which AB & CD are parallel sides and AD and BC are non parallel sides.

The area of trapezium is calculated using following formula;

Area = 1/2 x (sum of parallel sides) x height