1. Equations of Circles

2. You can write an equation of a circle in a coordinate plane, if you know: Its radius The coordinates of its center

3. Standard Equation of a Circle: is the center of the circle r is the radius of the circle.

4. If the center is the origin, then the standard equation is

5. To graph a circle on a coordinate plane: 1.Identify the center 2.Graph the center 3.Identify the radius

6. 4.Start at the center and count the number of units that the radius is above the center, below the center, to the left of the center and to the right of the center. 5.Draw the circle to connect those points.