8 7 Circles and Circumference A circle is

8 -7 Circles and Circumference Radius (plural: radii). A line segment with one endpoint

8 -7 Circles and Circumference A diameter is a chord that passes through the

8 -7 Circles and Circumference A chord is a line segment that has both

8 -7 Circles and Circumference Additional Example 1: Naming Parts of a Circle Name

8 -7 Circles and Circumference Check It Out: Example 1 Point D is the

8 -7 Circles and Circumference The distance around a circle is called the circumference.

8 -7 Circles and Circumference The ratio of the circumference to the diameter, C

8 -7 Circles and Circumference The decimal representation of pi starts with 3. 14159265.

8 -7 Circles and Circumference Additional Example 3 A: Using the Formula for the

8 -7 Circles and Circumference Additional Example 3 B: Using the Formula for the

8 -7 Circles and Circumference Check It Out: Example 3 A Find the missing

8 -7 Circles and Circumference Check It Out: Example 3 B Find the missing

8 -7 Circles and Circumference Lesson Quiz Find the circumference of each circle. Use

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8 -7 Circles and Circumference A circle is the set of all points in a plane that are the same distance from a given point, called the center. Center

8 -7 Circles and Circumference Radius (plural: radii). A line segment with one endpoint at the center of the circle and the other endpoint on the circle. Radius Center

8 -7 Circles and Circumference A diameter is a chord that passes through the center of the circle. Diameters are the longest chords in a circle. Radius Center Diameter

8 -7 Circles and Circumference A chord is a line segment that has both endpoints on the circle. Radius Center Chord Diameter

8 -7 Circles and Circumference Additional Example 1: Naming Parts of a Circle Name the circle, a diameter, and three radii. L Z M N

8 -7 Circles and Circumference Check It Out: Example 1 Point D is the center of the circle. Name the circle, two chords, a diameter, and three radii. I D H G

8 -7 Circles and Circumference The distance around a circle is called the circumference. Circumference Radius Center Diameter

8 -7 Circles and Circumference The ratio of the circumference to the diameter, C , is the same for any circle. This d ratio is represented by the Greek letter , which is read “pi. ” C = d

8 -7 Circles and Circumference The decimal representation of pi starts with 3. 14159265. . . and goes on forever without repeating. Most people estimate using either 3. 14 or 22. 7 The formula for the circumference of a circle is C = d, or C = 2 r.

8 -7 Circles and Circumference Additional Example 3 A: Using the Formula for the Circumference of a Circle Find the missing value to the nearest hundredth. Use 3. 14 for pi. d = 11 ft; C = ? 11 ft

8 -7 Circles and Circumference Additional Example 3 B: Using the Formula for the Circumference of a Circle Find each missing value to the nearest hundredth. Use 22/7 for pi. r = 7 cm; C = ? 7 cm

8 -7 Circles and Circumference Check It Out: Example 3 A Find the missing value to the nearest hundredth. Use 3. 14 or 22 for pi. 7 C=? D = 2. 8

8 -7 Circles and Circumference Check It Out: Example 3 B Find the missing value to the nearest hundredth. Use 3. 14 or 22 for pi. 7 r=? C = 88 cm C = 2πr 88 ≈ 2 22 __ r 7 88 ≈ 44 r 7 r ≈ 14 cm

8 -7 Circles and Circumference Lesson Quiz Find the circumference of each circle. Use 3. 14 for . 1. 8 in. 2. 3 in. 3. Find the circumference of a circle with a diameter of 20 feet. Use 3. 14 for .