The Area of a Circle, Sector and Annulus

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Saturday, 14 November 2009
The Area of a Circle, Sector and Annulus
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RADIUS The distance from the centre to the
edge DIAMETER The distance from one side to the
other passing through the centre Diameter is
twice the radius D 2 x R Radius is half the
diameter R D 2
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Calculate the area A ?r2 A 3.14 x r x r A
3.14 x 6 x 6 A 113.04 cm2
Radius 6cm
Calculate the radius r v(A ?) r v(25
3.14) r v7.962 r 2.82 cm
Area 25cm2
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Calculate the area A ?r2 A 3.14 x r x r A
3.14 x 10 x 10 A 314 cm2
Radius 10cm
Calculate the radius r v(A ?) r v(50
3.14) r v15.923 r 3.99 cm
Area 50cm2
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Radius 10cm
A Angle 360 x ?r2 A 72 360 x 3.14 x 10 x
10 A 0.2 x 314 A 62.8 cm2
720
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A Angle 360 x ?r2 A X 360 x 3.14 x r x
r A 0.2 x 314 A 62.8 cm2
X0
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A Angle 360 x ?r2 A X 360 x 3.14 x r x
r A 0.2 x 314 A 62.8 cm2
X0
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Area 150 360 x ? x 132 Area 4.166667 x 3.14
x 169 Area 221 cm2
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The area of an ANNULUS
For this example R 10 metres and r 5 metres
R
A p(R r)(R r) A 3.14 x 15 x 5 A 235.5
metres2
r
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Calculate the area of each annulus described in
the table.
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