A quadrilateral is a closed figure bounded by four line segments.
1. four vertices (A,B,C and D)
2. four sides (AB, BC, CD and DA)
3. four angles (∠A, ∠B, ∠C and ∠D)
4. two diagonals (AC and BD)

Two sides of a quadrilateral having a common end-point are called adjacent or consecutive sides. There are four pairs of it.
In the quadrilateral (AB,BC), (BC,CD), (CD,DA) and (DA,AB) are such sides.

### Opposite sides

Two sides of a quadrilateral having no common end-point are called opposite sides. There are two pairs of it.
In the quadrilateral (AB,CD) and (BC,DA) are such sides.

Two angles of a quadrilateral having a common side are called adjacent or consecutive angles. There are four pairs of it.
In the quadrilateral (∠A,∠B), (∠B,∠C), (∠C,∠D) and (∠D,∠A) are such angles.

### Opposite angles

Two angles of a quadrilateral having no common side are called opposite sides. There are two pairs of it.
In the quadrilateral (∠A,∠C) and (∠B,∠D) are such sides.

## Parallelogram

A quadrilateral in which opposite sides are parallel is called a parallelogram.
ABCD is a parallelogram. AB||CD and BC||DA.

## Properties of a parallelogram

• opposite sides are equal
• opposite angles are equal
• diagonals bisect the parallelogram

## Rectangle

A parallelogram in which all the angles are 90° is called a rectangle.
ABCD is a rectangle.

## Properties of a rectangle

• opposite sides are equal
• each angle measures 90°
• diagonals are equal

## Square

A rectangle in which all sides are equal is called a square.
ABCD is a square.

## Properties of a square

• all sides are equal
• each angle measures 90°
• diagonals are equal
• diagonals intersect at 90°

## Rhombus

A parallelogram in which all sides are equal is called a rhombus.
Ab=CD=DA=AB
ABCD is a rhombus.

## Properties of a rhombus

• opposite sides are parallel
• all sides are equal
• diagonals bisect each other at right angles

## Trapezium

A quadrilateral in which two opposite sides are parallel is called a trapezium.
ABCD is a Trapezium.
AB||DC.
If the non parallel sides are equal then the trapezium is called isosceles trapezium.