QUESTION 2
Easy
Calculate, correct to 3 significant figures, the circumference of a circle with: (i) radius 7 cm (ii) radius 10 cm (iii) radius 12 cm.
SOLUTION
1
(i) Radius = 7 cm
\(\begin{aligned} C &= 2πr \\ &= 2 × \frac{22}{7} × 7 \\ &= 44 \,cm\end{aligned}\)
The circumference of the circle with radius 7 cm, correct to 3 significant figures, is 44.0 cm.
2
(i) Radius = 10 cm
\(\begin{aligned} C &= 2πr \\ &= 2 × \frac{22}{7} × 10 \\ &= \frac{440}{7} \\ &= 62.8571 \,cm\end{aligned}\)
The circumference of the circle with radius 10 cm, correct to 3 significant figures, is 62.9 cm.
3
(i) Radius = 12 cm
\(\begin{aligned} C &= 2πr \\ &= 2 × \frac{22}{7} × 12 \\ &= \frac{528}{7} \\ &= 75.4286 \,cm\end{aligned}\)
The circumference of the circle with radius 10 cm, correct to 3 significant figures, is 75.4 cm.
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Final Answer :
(i) 44.0 cm
(ii) 62.9 cm
(iii) 75.4 cm
Concept Note
Circumference of a circle is given by
\(C = 2πr\)