year 8 maths

362 Chapter 6 Angle relationships and properties of geometrical figures 1
PROBLEM-SOLVING AND REASONING
7–8(½) 7–8(½), 9
7–8(½), 9
7 Find the value of a in these diagrams.
a
a°
b
40°
c
70°
a°
61°
a°
67°
d
40°
e
65°
a°
f
a°
117°
a°
37°
31°
g
290°
a°
h
a°
120°
85°
i
82°
a°
65°
8 Sometimes parallel lines can be added to a diagram to help find an
unknown angle. For example, ∠AOB can be found in the diagram at right
by first drawing the dashed line and finding ∠AOC (40°) and
∠COB (70°). So ∠AOB = 40° + 70° = 110°.
Apply a similar technique to find ∠AOB in these diagrams.
40°
O 40°
70°
70°
B
A
C
a
A
50°
O
80°
B
b
B
A
50° 45°
O
c
20°
B
O
110° A
d
B
O
147°
116° A
e
B A
f
26°
O
39°
B
155° 119°
O
A
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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