Year 9 Interactive Maths - Second Edition

Perimeter

Recall that:

Perimeter is the distance around a closed figure.

Perimeters can be measured in millimetres (mm), centimetres (cm), metres (m) and kilometres (km).  These units are related as follows:

Perimeters of the following figures are often required to solve real world problems.

Perimeter of a Square

Recall that:

The perimeter, P, of a square is given by the formula:

P = 4s

where s is the length of any side of the square.

Example 1

Find the perimeter of a square paddock of side 35 m.

Solution:

So, the perimeter is 140 m.

Perimeter of a Rectangle

P = 2(l + w)

where l is the length and w is the width of the rectangle.

Example 2

Find the perimeter of a rectangular field of length 50 m and width 40 m.

Solution:

So, the perimeter is 180 m.

Perimeter of a Triangle

P = a + b + c

where a, b and c are the side lengths of the triangle.

Example 3

Find the perimeter, P, of the triangle shown.

Solution:

So, the perimeter is 24 cm.

Key Terms

perimeter