year 8 maths

3C
Area
131
• Triangle A = 1 2 × b × h = 1 2 bh
The dashed line which gives the height is
perpendicular (at right angles) to the base.
h
b
Key ideas
■ Areas of composite shapes can be found
by adding or subtracting the area of more
basic shapes.
1
2
Example 6
Converting units of area
Convert these area measurements to the units shown in the brackets.
a 0.248 m 2 (cm 2 ) b 3100 mm 2 (cm 2 )
SOLUTION
a 0.248 m 2 = 0.248 × 10 000
= 2480 cm 2
b 3100 mm 2 = 3100 ÷ 100
= 31 cm 2
EXPLANATION
1 m 2 = 100 2 cm 2 = 10 000 cm 2
Multiply since you are changing
to a smaller unit.
1 cm 2 = 10 2 mm 2 = 100 mm 2
Divide since you are changing
to a larger unit.
m 2 ×100 2 cm 2
cm 2 mm 2
÷10 2
Example 7
Finding areas of rectangles and triangles
Find the area of these shapes.
a
2 cm
6 cm
b
7 m
13 m
SOLUTION
a
A = lb
= 6 × 2
= 12 cm 2
EXPLANATION
Write the formula for the area of a rectangle and
substitute l = 6 and b = 2 .
b
A = 1 2 bh
= 1 2 × 13 × 7
= 45.5 m 2
Remember that the height is measured using a
line that is perpendicular to the base.
Cambridge Maths NSW
Stage 4 Year 8 Second edition
ISBN 978-1-108-46627-1 © Palmer et al. 2018
Cambridge University Press
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