1. LT 11.8: Write equations and graph circles in the coordinate plane.

2. The equation of a circle is based on the Distance Formula and the fact that all points on a circle are equidistant from the center.

4. Example 1: Writing the Equation of a Circle
Write the equation of each circle.
J with center J (2, 3) and radius 4
(x - 2)2 + (y - 3)2 = 16

5. Example 2: Writing the Equation of a Circle
Write the equation of each circle.
K that passes through J(6, 4) and has center
K(1, –8)
JK =
(x - 1)2 + (y - 8)2 = 169

6. Example 3: Graphing a Circle
If you are given the equation of a circle, you can graph the circle by making a table or by identifying its center and radius.
Example 3: Graphing a Circle
Graph x2 + y2 = 16.

7. Example 4: Graphing a Circle
Graph (x – 3)2 + (y + 4)2 = 9.

8. Work with your partner to write these equations:
x2 + y2 = 100
(x + 1)2 + (y - 8)2 = 25
(x -5)2 + (y – 5)2 = 20
x2 + y2 = 85
x2 + (y + 2)2 = 40
(x -11)2 + (y – 4)2 = 170