Page 172 - Mathematics Coursebook

18.2 Calculating the area and perimeter of rectangles

18.2 Calculating the area and perimeter of rectangles

When you draw a rectangle on a centimetre square grid, you can
work out the area of the rectangle by counting squares.

Area = 6 cm 2 2 cm
Instead of counting squares, you can multiply the length of the
rectangle by its width to work out the area.
3 cm

2 cm

3 cm

Area = 3 × 2 = 6 cm 2
!e formula for working out the area of any rectangle is:

area = length × width w
or A = l × w l

!e perimeter of a shape is the total distance around the outside of the shape.

You "nd the perimeter of a shape by adding the lengths of all the sides together.

!e perimeter of this rectangle is: 3 cm
3 + 2 + 3 + 2 = 10 cm
You can see that you are adding two lengths and 2 cm 2 cm
two widths together.
!e formula for working out the perimeter of any rectangle is: 3 cm

perimeter = 2 × length + 2 × width

or P = 2l + 2w w

l
Worked example 18.2

Work out the area and the perimeter of this rectangle.
4 cm

6 cm
Solution
Area = 6 × 4 Use the formula: area = length × width.
2
= 24 cm Remember to write the correct units, cm , with your answer.
2
Perimeter = 2 × 6 + 2 × 4 Use the formula: perimeter = 2 × length + 2 × width.
= 12 + 8 Work out 2 × length and 2 × width fi rst, then add the answers.
= 20 cm Remember to write the correct units, cm, with your fi nal answer.

18 Area, perimeter and volume 171