1. GEOMETRY
Circle Terminology

2. Radius (or Radii for plural)
Definition:
The segment joining the center of a circle to a point on the circle.
Formula: 1/2 diameter
Example: OA

3. Diameter
Definiton:
A chord that passes through the center of a circle.
Formula:
2xradius
Example: AB

4. Chord
Defintion:
A segment joining two points on a circle
Example: AB

5. Central Angle Definition:
An angle whose vertex is at the center of a circle.
Example: Angle ABC

6. CIRCUMFERENCE Definition:
Circumference is the distance around the circle.
Example:
find the circumference of this circle……
Circumference= 2 X 4 X 3.14
C= cm
Formula:
Circumference = 2x radius x 2 π (OR pi x diameter)
Radius = 4cm

7. AREA OF CIRCLE FORMULA: PI X RADIUS SQUARED DEFINITION:
THE AMOUNT OF SQUARE UNITS INSIDE THE CIRCLE
EXAMPLE:
RADIUS - 3IN
AREA = PI (3.14) X 3squared=
3.14 x 9=28.26sq in
FORMULA:
PI X RADIUS SQUARED

8. PRACTICE!!! Write answers on your paper- then we will check in 5 mins
1) RADIUS= 4CM, WHAT IS THE DIAMETER?
2) DIAMETER= 44IN, WHAT IS THE RADIUS?
3) Diameter = 3in, what is circumference? (use 3.14 for pi and use a calc)
4) Diameter= 5cm, what is radius?
5) Diameter 10cm, what is circumference? (use calc)