1. CIRCLES
Topic 7.3

2. Definitions
Circle: The set of all points that are the same distance from the center
Radius: a segment whose endpoints are the center and a point on the circle

3. Equation of a Circle

4. Writing the Equation of a Circle
Group x terms together, y-terms together, and move constants to the other side
Complete the square for the x-terms
Remember that whatever you do to one side, you must also do to the other
Complete the square for the y-terms

5. Example: Write the equation and find the center and radius length of :
Group terms
Complete the square

6. You try!!: Write the equation and find the center and radius length of :

7. THINK ABOUT IT
Find the center, the length of the radius, and write the equation of the circle if the endpoints of a diameter are (-8,2) and (2,0).
Center: Use midpoint formula!
Length: use distance formula with radius and an endpoint
Equation: Put it all together