1. C IRCLES

2. http://www.youtube.com/watch?v=FbUPyUi5YtM &feature=related

3. P ARTS OF CIRCLE C F E AB P Name a circle by its center. P CP is radius AB is Diameter EF is a chord Note: AB is also a chord.

4. D EFINITIONS Radius: is a segment w/one endpoint at the center of the circle and the other endpoint on the circle. All radii of a circle are congruent. Chords: are segments that have both their endpoints on the circle. (i.e. it goes from one side of the circle to the other.) Diameter: a chord that goes through the center of a circle.

5. T HE CENTER OF A CIRCLE IS THE MIDPOINT OF THE DIAMETER Ex: is a diameter of the circle. Find the coordinates of the center and the length of the radius of the circle. Center (P) = Midpoint of the diameter  Use Midpoint Formula Radius is the distance from the center to any point on the circle.  Use Distance Formula to find the radius. B(5, 4) A(-3, 2)

6. F ORMULAS All radii are congruent All diameters are congruent d = 2r and r = d/2 or ½ d Ex: a. If DF = 10, find DA b. If PA = 7, find PG c. If AG = 12, find LA A FG L D P

7. C IRCUMFERENCE The circumference of a circle is the distance around the circle. (To find circumference you have to walk on the edge)(example – carousel) Formulas: C =  d or C = 2  r Note :  (pi) has a key on the calculator; accepted value: 3.14 Ex: Find the circumference, diameter and radius. a) Find C if r = 7cm b) Find C if d = 12.5 in c) Find d and r to the nearest hundredth if c = 136.9 meters. 7cm12.5 in

8. Y OU CAN ALSO USE GEOMETRIC FIGURES TO HELP YOU FIND THE CIRCUMFERENCE OF A CIRCLE Find the exact circumference of P. Ex: P 5 12 the diameter, x = _______ the exact circumference = _______ the approximate circumference = _______ (to the nearest tenth)