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## Arc Lengths

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**Arc Lengths**Sections 10.2 and 11.4**Circumference**• The circumference of a circle is found by using the formula C = 2πr • Arc length is a part of the circumference of a circle and is found by using a proportion. Arc Length**Central Angle**• A central angle of a circle is an angle whose vertex is the center of the circle. • When we say the measure of an arc, we are referring to the degree measure. • When we say the length of the arc, we are referring to the portion of the circumference the arc covers. Measure of an Arc Length of an Arc**Notation**• When naming an arc, for instance arc AB, we use the notation • When talking about the degree measure of an arc, we use the notation**Minor Arc**• The measure of a minor arc is the measure of its centralangle. • The measure of the entire circle is 360o. The measure of a major arc is the difference between 360o and the measure of the related minor arc. Major Arc**Semicircle**• A semicircle is an arc whose endpoints are the endpoints of a diameter.**Arc Addition Postulate**• The measure of an arc formed by two adjacent arcs is the sum of the measures of the two arcs**Find the measure of each indicated arc below for circle P**shown**Congruent Circles**• Two circles are congruent circles if they have the same radius. • Two arcs are congruent arcs if the have the same measure and they are arcs of the same circle or of congruent circles. Congruent Arcs**Assignment**• P. 661 #1-17, 21, 25(a)