9.1.2 Developing Formulas for Circles and Regular Polygons (continued)
The circumference of a circle is determined in this example. The area of the circle is given as an algebraic expression. Begin by determining the length of the radius of the circle from the expression for the area. Substitute the expression for the area into the formula for the area of a circle and isolate r . The value of r is found to be 2 x . Substitute the value for r into the formula for the circumference of a circle. The solution yields C = 4 πx meters for the circumference. The areas of three circles are determined in this application example. The diameters of each of the circles are given. Divide each diameter by 2 to find the length of the radius of each of the circles. Then substitute the length of the radius into the formula for the area of a circle. Use a calculator to find the actual area in square inches. The three circles have areas 12.6 in 2 ( r = 2 in.), 50.3 in 2 ( r = 4 in.), and 78.5 in 2 ( r = 5 in.).
Example 2 Cooking Application
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