circumference

• Pi

  A special ratio used to calculate the circumference and area of circles
• Calculating circumference

  Circumference = Pi x diameter
• Calculating area

  Area = Pi x radius^2
• Diameter


  2 x radius
• Squaring a number means multiplying it by itself
• r^2 is not the same as 2 x r
• Circle with radius of 8 meters


  • Circumference = Pi x 2 x 8 = 50.24 meters

  Area = Pi x 8^2 = 200.96 square meters
• Circumference is a 1-dimensional quantity, area is a 2-dimensional quantity
• Circumference of the Earth

  • Diameter = 12,750 km, Circumference = 40,055 km
• Area of a 24-inch diameter pizza

  • Radius = 12 inches, Area = Pi x 12^2 = 452.16 square inches
• solve with the formula of area and circumference

  c = PI x d a = PI x r (2)

  8 x 2 = 16m 8 x 8 = 64m(2)

  16 x 3.14 64 x 3.14

  c = 50.24m a = 200.96m(2)