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1. October 4, 2012
Circles
2. The area of a circle.
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2. Explanation October 4, 2012
Here is a circle.You can divide it into sectors.
The sectors can be rearranged, to form a shape very
close to a rectangle.
The two long edges are made up from the circumference,
which is π × d
One side is made up from π × d ÷ 2 which is π × r
Each of the short sides is made up from the radius.
The area can now be calculated as π × r × r or π r ²
π×r
r
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3. Example October 4, 2012
The second hand on a clock is 11cm long.
What is the area of the clock face it
passes over in one minute?
A = πr ²
A = π × 11²
A = π × 121
A = 380.1327…
The area the second hand covers is is 380cm ² , to 3 s.f.
In this case, it is sensible to give an answer to the
nearest cm ².
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4. Example October 4, 2012
A circular office carpet has a diameter of 1.8m.
Calculate its area. A = πr ²
Calculate the radius. r = 1.8 ÷ 2 = 0.9 A = π × 0.9 ²
A = π × 0.81
A = 2.54690…
The carpet is 2.54m² , to 2 d.p.
It is sensible to give an answer
to the nearest cm².
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