## Definition

A plane figure with four straight sides making four right
internal angles.

## Properties

- Has four sides and four angles; in ▭ ABCD, AB, BC, CD, and DA are four sides and ∠ABC, ∠BCD, ∠CDA, ∠DAB are four angles
- Opposite sides are equal; so AB = CD and BC= DA
- Opposite sides are parallel; AB ∥ CD and BC ∥ DA
- All the angles are 90°; in ▭ ABCD, ∠ABC = ∠BCD = ∠CDA =∠DAB = 90°
- The diagonals are equal and bisect each other; so AC = BD
- The sum of the interior angles is equal to 360 degrees; ∠ABC + ∠BCD + ∠CDA + ∠DAB = 360°

## Formulas

### Diagonal

The line segments linking opposite vertices or corners of
the rectangle. The formula is given below:

**Problem**: Finding the diagonal of a rectangle when the **WIDTH **and** LENGTH** are known

**Find the diagonal of a rectangle whose width is 12 cm and length is 5 cm.**

Solution:

As we know,

**Diagonal (***d* ) = √(*w*^{ 2} + *l*^{ 2}), where *w* = 12 cm and *l* = 5 cm

= √(12^{2} + 5^{2})

=√(144 + 25)

= √169

= 13 cm

### Area

The total space enclosed by
the rectangle. The formula is given below:

**Problem**: Finding the area of a rectangle when the **WIDTH **and** LENGTH** are known

**Find the area of a rectangle whose width is 10 cm and length is 6 cm.**

Solution:

As we know,

**Area (***A*) = *w* × *l*, where *w* = 10 cm and *l* = 6 cm

= 10 × 6 cm

= 60 cm^{2}

### Perimeter

The total distance covered around the edge of the rectangle. The
formula is given below:

**Problem**: Finding the perimeter of a rectangle when the **WIDTH **and** LENGTH** are known

**Find the perimeter of a rectangle whose width is 7 cm and length is 9 cm.**

Solution:

As we know,

**Perimeter (***P* ) = 2 (*w* + *l* ), where*w* = 7 cm and *l* = 9 cm

= 2(7 + 9) cm

= 2 × 16 cm

= 32 cm