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Area of a circle



The formula for the area of a circle is:    A = pi × r2

If r is known, simply substitute the known value for r in the formula. Use 3.14 for pi.

Examples

1) Calculate A if r = 4 inches

A = pi × r2 = 3.14 × 42 = 3.14 ×16 = 50.24 inches2

Notice that the unit (inches) is squared to show that it was multiplied by itself twice

2) Calculate A if r = 6 inches

A = pi × r2 = 3.14 × 62 = 3.14 ×36 = 103.04 inches2

If A = 78.5 inches2, find r


Review Solving multiplication equations before looking at the solution below.



r = 5 inches because 52 = 5 × 5 = 25


Use the calculator below to find the area


Enter the radius of the circle:     

      

The area is :  




Circle| The number pi| Circumference of a circle| Area of a circle| Home page






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