1. © 2010 Pearson Prentice Hall. All rights reserved Circles § 7.7

2. Tobey & Slater, Basic College Mathematics, 6e2 Center Radius and Diameter A circle is a figure in which all points are at an equal distance from a given point. Radius Diameter Center Diameter = 2  radius d = 2r

3. Tobey & Slater, Basic College Mathematics, 6e3 Circumference The distance around a circle is called the circumference. Pi, denoted by the symbol , is the number we get when we divide the circumference of a circle by its diameter.   3.14

4. Tobey & Slater, Basic College Mathematics, 6e4 Circumference The circumference of a circle can be found by multiplying the length of the diameter times . C =  d Example: Find the circumference of a circle whose diameter is 5 inches. C =  d = 3.14(5) = 15.7 The circumference is approximately 15.7 inches.

5. Tobey & Slater, Basic College Mathematics, 6e5 Area The area of a circle is the product of  times the radius squared. A =  r 2 Example: Find the area of a circle whose radius is 15 feet. The area is approximately 706.5 ft 2. A =  r 2 = (3.14)(15 ft) 2 = (3.14)(225 ft 2 ) = 706.5 ft 2

6. Tobey & Slater, Basic College Mathematics, 6e6 Solving Area Problems Example: Find the area of the shaded region. Area of shaded = area of rectangle + area of semicircle 10 ft 18 ft Half of a circle (18)(10) = + 180 = + 219.25 ft 2 = = lw + r2r2 Area  1839.25 ft 2 Half of a circle