1. Circle Unit
Chapter 9

2. Definitions
A circle is the set of all points in a plane that are equidistant from a given point in the plane known as the center of the circle.
A radius (plural, radii) is a segment from the center of the circle to a point on the circle.
A chord is a segment whose endpoints lie on a circle.
A diameter is a chord that contains the center of a circle.
A central angle is an angle formed by two rays originating from the center of a circle (2 radii)
An arc is an unbroken part of a circle (along the circumference)

3. All the parts to a circle…

4. 3 types of Arcs Semicircle: endpoints are the endpoints of a diameter
Usually use 3 letters to write the name of a semicircle
Ex: 𝑀𝑂𝑁 , 𝑁𝐿𝑀
Minor Arc: shorter than a semicircle
Usually use 2 letters to write the name of a minor arc
Ex: 𝑀𝑂 , 𝐿𝑀
Major Arc: longer than a semicircle
Usually use 3 letters to write the name of a major arc
Ex: 𝑀𝐿𝑂 , 𝑁𝑀𝐿

5. Intercepted Arc:
An arc whose endpoints lie on the sides of the angle and whose other points lie in the interior of the angle.

6. Measuring Arcs in Terms of Degrees
Semicircle = 180 because it is half of the distance around the circle
𝐴𝐶𝐵 =180°
Minor Arc = measure of its central angle
𝐶𝐵 =35°
Major Arc = 360 - measure of its minor arc
𝐶𝐷𝐵 =360°−35°=325°

7. Practice
Find m 𝐴𝐶
Find m 𝐴𝐵𝐶

8. “Prizes”
10 tickets = 1 point on test/project (f/ Q4) 30 tickets = 100 homework grade 40 tickets = 100 quiz grade 150 tickets = 100 test/project grade 1-9 tickets left over = 2 pieces of candy