1. Circumference and Area: Circles

2. Formulas
C = πd or 2πr
A = πr2

3. Definitions:
Circle- the set of all points in a plane that are the same distance from a given point, called the center.

4. The distance from the center to any point on the circle is called the radius.

5. The length of the radius is equal to ½ the length of the diameter.

6. The distance across the circle through its center is the diameter.

8. The circumference is the distance around the circle.

9. pi ( ): A number, 3.141592..., equal to (the circumference) / (the diameter) of any circle.

10. For any circle with a diameter, d the circumference, C is found by using this formula

11. Remember that, for any circle, the diameter is twice the radius or d = 2r.
If we are told the radius instead of the diameter we use the formula:

12. The circumference of a circle is the product of pi and the diameter (or twice the radius).

13. The area of a circle is the product of pi and the square of the radius.

15. Arc- a curved line that is part of the circumference of a circle.

16. Chord- a line segment within a circle that touches 2 points on the circle
Diameter is a special chord that goes through the center.