year 8 maths

3B
Circumference of circles
129
17 We know that C = 2πr or C = πd .
a Rearrange these rules to write a rule for:
i r in terms of C ii d in terms of C
b Use the rules you found in part a to find the following, correct to two decimal places.
i the radius of a circle with circumference 14 m
ii the diameter of a circle with circumference 20 cm
ENRICHMENT
– –
18
Memorising pi
18 The box shows π correct to 100 decimal places. The Guinness World record for the most number
of digits of π recited from memory is held by Rajveer Meena, an Indian student. He recited
70 000 digits, taking nearly 10 hours.
3.1415926535 8979323846 2643383279 5028841971 6939937510
5820974944 5923078164 0628620899 8628034825 3421170679
Challenge your friends to see who can remember the most number of digits in the decimal
representation of π .
Number of digits memorised
Report
10+ A good show
20+ Great effort
35+ Superb
50+ Amazing memory
Cambridge Maths NSW
Stage 4 Year 8 Second edition
ISBN 978-1-108-46627-1 © Palmer et al. 2018
Cambridge University Press
Photocopying is restricted under law and this material must not be transferred to another party.