Using a formula to fi nd the area of rectangles and squares
Sometimes it is easier to fi nd the area of a rectangle or square if we use a formula. In the diagram on the right, we can count up the number of squares to fi nd the length, similarly we can count across the number of squares to fi nd the width.
Area of a rectangle = length × width
By multiplying the length by the width, we can fi nd the area. In this case: area = 6 × 4 = 24 square units
Worked example 1 Find the area of the following shapes.
(i) Width = 4 cm Length = 9 cm
Solution (i)
Width = 3 units (ii) Length = 7 units
2 3 4 5 6 7 8 9
1 0 Width = 4 units
Length = 6 units 1 2 3 4 5 6 7 8 9 x
(ii)
Perimeter of a rectangle
We can also use a formula to fi nd the perimeter of a rectangle or square. In the diagram on the right, we can count the number of squares to fi nd the width, and we can count the number of squares across to fi nd the length.
Perimeter of a rectangle = length + width + length + width
By adding the lengths to the widths, we can fi nd the perimeter.
In this case: Perimeter = 6 + 4 + 6 + 4 = 20 units
2 3 4 5 6 7 8
Length = 6 units
0 1
1 2 3 4 5 6 7 8 9 x
y
Section A Introducing concepts and building skills