**Key Terms**

- Arc – A part of the circumference of a circle.
- The symbol means “the arc with endpoints A and B.”

- Central Angle – An angle that has its vertex at the center of the circle.
- Major Arc – An arc of a circle that is longer than half the circumference.
- The degree measure of a major arc is greater than 180°

- Minor Arc – An arc of a circle that is shorter than half the circumference.
- The degree measure of a minor arc is less than 180°.

- Semicircle – A 180° arc; half of a circle.

**Review**

- Play the circle review game on Pg 1 in Apex Study 6.3

**Notes**

- Arcs
- Like a line segment, an arc has a point at each end, called an endpoint.

- Central Angles
- An angle whose vertex is at the center of a circle.
- The sides of a central angle are two radii of the circle.
- The sides of a central angle (the radii) intercept the circle and form an arc.
- To intercept means “to intersect,” “to stop the course of,” or “to mark off.”
- It stops the course of the arc around the circumference of the circle.
- It marks off the length of the arc

- Minor Arc
- An arc that lies between the two sides of a central angle that measures less than 180°.
- Notation: <– The arc above AB should look more curvy (like the one below)

- An arc that lies between the two sides of a central angle that measures less than 180°.

- Major Arc
- A major arc lies outside of the central angle that is created by a minor arc, and it measures more than 180°.
- The middle point in a major arc name is a point on the arc between its two endpoints.
- Notation: <– The arc above AXB should look more curvy (like the one below)

- A major arc lies outside of the central angle that is created by a minor arc, and it measures more than 180°.

- Semicircle
- An arc that measures 180° created by the diameter’s endpoints.

**Examples**

- Ex 1. Given below, is a minor arc, a major arc, or a semicircle?
- Because it is less than 180°, it is a minor arc.

- Ex 2. What is the measure of in below?
- Since circles have a total degree measure of 360°, you must subtract the minor arc (given: 30°) from 360° to find the major arc.
- Answer: 330°