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Area of a Circle


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Area of a Circle

  1. 1. A circle is a 2-dimensional shape which made by drawing a curve that has always the same distance from the center. It is one of the basic shape in geometry
  2. 2. Circumference: The distance around the circle; a special name for the perimeter of a circle  Arc: A part of the circumference  Radius: The distance from the centre to the circumference  Diameter: the distance from side to side passing though the centre; the greatest with of a circle 
  3. 3. The formula: A = π × r2 Π= *It is very important to know either the Radius or the Diameter in order to take out the area of a circle*
  4. 4. Ex 1 Ex 2 r=4cm d=6cm So, r=3cm A = π × r2 A= x 42 A = π × r2 A= A= x 32 x 16 ~ 5.28 A= x 9 ~ 28.28
  5. 5. To find an area of an Irregular shape, Separate each shape to find its area Example A sports ground Rectangle A=wxh, so 60×40=2400m2 Circle d=40m, so r=20m A=πr2=π×202=400π=1256m2 Irregular Shape 2400m2+1256m2=3656m2 40m 60m 40m Note π=3.14 d÷2=r A=πr2=πxr2 A=wh=wxh 40m 60m
  6. 6. Thank you