1. 9-1 Exploring Circles Objectives: To identify and use parts of circles. To solve problems involving the circumference of a circle.

2. Vocabulary Circle Center Radius Chords Diameter Circumference π (pi)

3. Vocabulary A circle is the set of all points in a plane that are a given distance from a given point in the plane. That point is the center of the circle.

4. Vocabulary A radius of the circle is a segment that one endpoint at the center of the circle and the other endpoint on the circle. All radii are congruent to each other.

5. Vocabulary A chord of a circle is a segment that has its endpoints on the circle. RF and KL are both chords of Circle P. KL is also a diameter of Circle P.

6. Circumference of Circle If a circle has a circumference of C units and a radius of r units, then C = 2πr.

7. Example 1 Find the circumference of a circle with a radius of 6.8 centimeters.

8. Example 2 Find the exact circumference of Circle P.