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Area of a Circle Part II Unit 2 > Lesson 3 of 6


Example 1: The radius of a circle is 3 inches. What is the area? [IMAGE]
Solution: A = Pi times r times r
  A = 3.14 · (3 in) · (3 in)
  A = 3.14 · (9 in2)
  A = 28.26 in2

Example 2: The diameter of a circle is 8 centimeters. What is the area? [IMAGE]
Solution: [IMAGE]
  8 cm = 2 · r
  8 cm ÷ 2 = r
  r = 4 cm
  A = Pi times r times r
  A = 3.14 · (4 cm) · (4 cm)
  A = 50.24 cm2

Example 3: The area of a circle is 78.5 square meters. What is the radius? [IMAGE]
Solution: A = Pi times r times r
  78.5 m2 = 3.14 · r · r
  78.5 m2 ÷ 3.14 = r · r
  25 m2 = r · r
  r = 5 m



Summary Given the radius or diameter of a circle, we can find its area. We can also find the radius (and diameter) of a circle given its area. The formulas for the diameter and area of a circle are listed below:
[IMAGE]
A = Pi times r squared  or  A = Pi times r times r



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Last Modified 18 May 2012