1. 9-8 Equations of Circles Objectives: To write and use the equation of a circle in the coordinate plane.

2. Vocabulary

3. Standard Equation of a Circle In general, an equation for a circle center at (h, k) and a radius of r units is: (x – h) 2 + (y – k) 2 = r 2 Please note that the minus signs are part of the equation.

4. Example 1 Write an equation for a circle with center C(-3, 6) and diameter of 6 units. (x – h) 2 + (y – k) 2 = r 2

5. Example 2 Graph the circle whose equation is (x + 2) 2 + (y – 3) 2 = 9