2. A Circle is a closed plane figure in which all the points are the same distance from the center. F Center Circle F

3. A Chord is a line segment that connects two points on a circle. Y B C D A Chords: AB AC AD

4. The Diameter of a circle is a special chord that passes through the center of a circle. E B C D A Diameter: AC

5. The Radius of a circle is a line segment from the center of the circle to any other point on the circle. Y B C D A Radii: YA YC YD (plural form of radius)

6. diameter radius The length of the radius is one half the length of the diameter. If r = 2 cm, then d = 4 cm. d = 2 x r or r = d ÷ 2 d (diameter) r (radius) If d = 5 in, then r = 2.5 in.

7. You can use a compass to construct a circle. Step 1: Open the compass to the length of the radius. Step 2: Put the tip of the compass at a point to be the center. Step 3: Rotate the pencil around the center. P compass

8. The Circumference is the distance around a circle. C (circumference)

9. The Circumference of a circle is greater than its diameter. It is always the same number of times as great. This number is called pi and is represented by the symbol π. ( π  3.14) You can find the circumference by multiplying π times the diameter. ( C = π x d )

10. C = π x d = 3.14 x 8 = 25.12 cm 8 cm E F G d = 8 cm The circumference is 25.12 cm.

11. C = π x d C = 2 x π x r = 2 x 3.14 x 3 = 18.84 in 3 in S T r = 3 in The circumference is 18.84 in. Remember: d = 2 x r

12. C = 62 m Find the diameter (d) to the nearest hundredth. C = π x d 62 = 3.14 x d 62 ÷ 3.14 = d d = 19.75 The diameter is 19.75 m. diameter

13. C = 52 in Find the radius (r) to the nearest hundredth. C = π x d 52 = 2 x 3.14 x r 52 = 6.28 x r r = 52 ÷ 6.28 The radius (r) is 8.28 in. C = 2 x π x r radius