1. Do NowDo Now
Copy this figure.Copy this figure.
Name everything that you see.Name everything that you see.
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A
R
B
S
T
O

2. ObjectiveObjective
 Go over the Basic Definitions for CirclesGo over the Basic Definitions for Circles
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3. Central AngleCentral Angle
 A Central Angle of a Circle is any angleA Central Angle of a Circle is any angle
with its vertex at the center.with its vertex at the center.
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4. ArcArc
 The set of points on a circle which lie in theThe set of points on a circle which lie in the
interior of a particular angle is called an arcinterior of a particular angle is called an arc
intercepted by an angle. If the central angle isintercepted by an angle. If the central angle is
then we would say “the arc STthen we would say “the arc ST
intersected byintersected by ”.”.
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SOT∠
SOT∠
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5. ChordChord
 A Chord is a segment that has twoA Chord is a segment that has two
endpoints on the edge of the circle.endpoints on the edge of the circle.
 Any Chord that goes through the center isAny Chord that goes through the center is
a diameter.a diameter.
SR
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A
B
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6. Name parts a - hName parts a - h4 – 27 – 09

7. Try to Prove this.Try to Prove this.