2. Definition: A circle is the set of all points on a plane that is a fixed distance from the center.

3. Circumference of a circle is the length around it, also known as the perimeter. Diameter of a circle is the length of the line through the center and touching two points on its edge.

4. Radius of a circle is the length of the line from the center to any point on its edge. Area of a circle is the number of square units inside of it.

5. The circumference of a circle can be calculated from its diameter using the formula : Circumference = pie x diameter ( pie = 3.14 ) ( pie = 3.14 )

6. Example : 18.84 = 3.14 x 6 3.14 6 is the diameter x 6 6 is the diameter x 6 3.14 is pie 18.84 3.14 is pie 18.84

7. The diameter of a circle can be calculated using the following formula: Diameter = 2 x radius (r)

8. Example : 20 = 2x 10 (r) 20 is the diameter 20 is the diameter 10 is the radius ( ½ diameter) 10 is the radius ( ½ diameter) 10 10 x 2 x 2 20 20

9. The radius of a circle can be calculated using the following formula: Radius = diameter / 2

10. Example: 5 = 10 / 2 10 is the diameter 10 is the diameter ( radius ) 5 is half 10 (diameter) ( radius ) 5 is half 10 (diameter)

11. r = 6