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.

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