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October 4, 2012

         Circles



2. The area of a circle.




                                     Next
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




                                                    More
                                                    Next
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.
                                                        More
                                                        Next
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.


                                                           More
                                                           Next
                                                           End

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Circles area

  • 1. October 4, 2012 Circles 2. The area of a circle. Next
  • 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 More Next
  • 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. More Next
  • 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. More Next End