1. 9.3 Circles Objective: Students identify parts of a circle and find central angle measures.

2. Vocabulary O Circle- the set of all points in a plane that are the same distance from a given point, called the center of a circle. O Arc- Part of a circle names by its endpoint. O Radius- line segment whose endpoints are the center of a circle and any point on the circle. O Diameter- Line segment that passes through the center of a circle, and whose endpoints lie on the circle. O Chord- line segment whose endpoints are any two points on a circle. Arc Diameter Radius Chord

3. Identify Parts of Circles O Name the parts of circle P. B C D P A A. radii B. diameter C. chords

4. More Vocabulary O Central angle- of a circle is an angle formed by two radii. O Sector- of a circle is the part of the circle enclosed by two radii and an arc connecting them. Central Angle Sector

5. Finding Central Angle O The total angle measure of a circle is 360°. O Take the percentage of the sector and multiply it by 360. 32% of 360 0.32 · 360 115.2°