1. Parts of a Circle

2. 42 (5)(3)2 29 – 52 Simplify. Calculate the area. 9.1 cm 21 km 4 cm

3. Center: The middle of a circle.
The set of all points the same distance from a point called the center.
Center: The middle of a circle.
Radius: The distance from the center of a circle to any point on the edge.
Chord: A line segment with endpoints on the circle.
Diameter: The distance across a circle through the center.

4. Central Angle:
An angle with its vertex at the center of the circle.

5. Videos ~ SAV Lesson 3 ~ Parts of circle
animated characters:
Kids:

6. Example 1 Use  C to name each circle part. A chord AB or EF A radius
CD or CE or CF
A diameter EF
Central Angle
∠ECD or ∠FCD or ∠FCE

7. Example 2 The diameter of a circle is 12 centimeters. Find the radius.
Radius is half the diameter ÷ 2 = 6
The radius is 6 cm.
The radius of a circle is 7 inches. Find the diameter.
Diameter is double the radius. 7•2 = 14
The diameter is 14 inches.

8. Example 3 Find the measure of the missing central angle.
The sum of the central angles is 360.
Write an equation x = 360
Combine like terms x = 360
Subtract – – x = 80
The missing central angle , x, is 80⁰.

9. How many degrees are in a circle? Name the longest chord in A.
Draw M with radius AM, diameter PR and chord XY.

10. Communication Prompt
Why is the diameter the longest chord in a circle?
Why is proper notation important?