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

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

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

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

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