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9.1 ~ Chords & Arcs. All about Circles. Circle : the set of all points in a plane equidistant from a center point Radius : a segment from the center of the circle to a point on the circle Chord : a segment whose endpoints lie on the circle
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All about Circles • Circle: the set of all points in aplane equidistant from a center point • Radius: a segment from the center of the circle to a point on the circle • Chord: a segment whose endpoints lie on the circle • Diameter: a chord containing the center of the circle
Angles & Arcs • Arc: an unbroken part of a circle • Minor arc: an arc that is less than a semicircle, or less than 180° (use 2 letters) • Major arc: an arc that is more than a semicircle, or more than 180° (use 3 letters and go the long way) • Semicircle: an arc whose endpoints are the endpoints of the diameter, exactly 180° (use 3 letters to denote which one – there are two)
Angles & Arcs • Central Angle: an angle whose vertex is the center of the circle • Intercepted arc: an arc whose endpoints lie on the sides of the angle and whose other points lie in the interior of the angle (#9)
Circles S R T P W Z Y
More Angles & Arcs • Degree measure of arcs • The degree measure of an arc is equal to the degree measure of the central angle that intercepts it • Arc Length
More Angles & Arcs • Find the measure and length of the following arcs D E X C A B
Measure and Length • Degree measure of an arc is a portion of the entire circle • Length of the arc is a portion of the circumference or edge of the circle
Chords & Arcs Theorem • In a circle (or in congruent circles), the arcs of congruent chords are congruent.(#1)