1. <APB is a Central Angle
Central Angle : An Angle whose vertex is at the center of the circle A
Major Arc
Minor Arc
More than 180°
Less than 180°
ACB P AB
To name: use 3 letters C
To name: use 2 letters B
<APB is a Central Angle

2. Semicircle: An Arc that equals 180°
To name: use 3 letters E D
EDF P F

3. THINGS TO KNOW AND REMEMBER ALWAYS
A circle has 360 degrees
A semicircle has 180 degrees
Vertical Angles are Congruent

4. measure of an arc = measure of central angle
96 Q
m AB =
96° B C
m ACB =
264°
m AE =
84°

5. Arc Addition PostulateB
m ABC =
+ m BC
m AB

6. 240 260 m DAB = m BCA = Tell me the measure of the following arcs. D
140
260
m BCA = R
40
100
80 C B

7. CONGRUENT ARCS
Congruent Arcs have the same measure and MUST come from the same circle or of congruent circles. C B D 45 45
110 A