year 8 maths

132 Chapter 3 Measurement and Pythagoras’ theorem
Example 8
Finding areas of composite shapes
Find the area of these composite shapes using addition or subtraction.
a
4 m
b
6 m
3 mm
10 m
1 mm
1.2 mm
SOLUTION
a
A = lb − 1 2 bh
= 10 × 6 − 1 2 × 10 × 4
= 60 − 20
= 40 m 2
b A = S 2
+ lb
= 3 2 + 1.2 × 1
= 9 + 1.2
= 10.2 mm 2
EXPLANATION
The calculation is done by subtracting the area of
a triangle from the area of a rectangle.
Rectangle − triangle
10 m
6 m
10 m
4 m
The calculation is done by adding the area of a
rectangle to the area of a square.
A 1
A 2
Area = A 1
+ A 2
Exercise 3C
REVISION
UNDERSTANDING AND FLUENCY
1–3, 4–6(½) 2, 3, 4–6(½)
5–6(½)
1 By considering the given diagrams, answer the questions.
a i How many mm 2 in 1 cm 2 ?
ii How many mm 2 in 4 cm 2 ?
iii How many cm 2 in 300 mm 2 ?
1 cm = 10 mm
1 cm =
10 mm
Diagram not to scale
b i How many cm 2 in 1 m 2 ?
ii How many cm 2 in 7 m 2 ?
iii How many m 2 in 40 000 cm 2 ?
1 m = 100 cm
1 m 2
1 m = 100 cm
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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