1. Advanced Algebra Trigonometry Appendix B
Objective:
SWBAT graph and learn about the equations of circles

2. The distance from the center is called the radius.
Definition of a Circle
A circle is a set of points a given distance from one point called the center.
The distance from the center is called the radius.

3. Circle
Below is a circle with radius 3 with the center at the origin. To find the equation of this circle, we let (x,y) be any point on the circle. Use the distance formula to plug in the information we know 
D = 2 -7 -6 -5 -4 -3 -2 -1 1 5 7 3 4 6 8
( x1, y1 ) = ( 0, 0 )
( x2, y2 ) = ( x, y )
* The distance equals the radius 3. *
(x, y)

4. Equation of a Circle The center of a circle is given by (h, k)
The radius of a circle is given by r
The equation of a circle in standard form is
(x – h)2 + (y – k)2 = r2

5. Finding the Equation of a Circle
If you have the center and the radius of the circle, plug it into the equation.
Center = (h, k) = ( 3 , 6 ) radius = 4
( x - h )² + ( y – k )² = r²
( x - 3 )² + ( y – 6 )² = 4²
( x - 3 )² + ( y – 6 )² = 16

6. Finding the Equation of a Circle
Find the equation of a circle with:
Center = (h, k) = (-5 , 0) radius = 8
Center = (h, k) = ( 3 , 9) radius = 5
Center = (h, k) = ( -5 , 3) radius = 2

7. Graphing a Circle
Graph the circle:
( x – 11 )² + ( y – 8 )² = 25

8. Homework
Page 450 # (all)