1. Sect. 12-1 Circles in the Coordinate Plane Geometry Honors

2. What and Why? What? – Write the equation of a circle. – Use the equation of a circle to solve real world problems. Why? – To investigate situations in which equations of circles can be used, such as expressing the range of cellular telephone towers.

3. Distance Formula

4. Theorem 12-1 Equation of a Circle

5. Example

6. When you make a call from your cell phone, a tower receives the call. In the graph, the center of each circle is the location of a cell tower. The equation of a circle can describe the receiving and transmitting range of a tower. Find the equation that describes the position and the range of Tower A.

7. Example If you know the center of a circle and a point on the circle, you can write the equation of the circle. Write an equation of the circle with center (1, -3) that passes through the point (4, 2).

8. Example

9. Write an inequality for the given graph.

10. Example A diameter of a circle has endpoints (-3, 7) and (5, 5). Write an equation of the circle.