1. 1.8 Circles

2. A circle is a set of points in the xy-plane that are a fixed
distance r from a fixed point (h,k).
The fixed distance is called the radius, and the fixed
point (h,k) is called the center of the circle. y
(x, y) r
(h, k) x

3. The standard form of an equation of a circle with radius r and center (h,k) is

4. Graph ( ) x y + - = 1 3 16 2

5. y
(-1, 7)
(3,3)
(-5, 3)
(-1,3) x
(-1, -1)

6. The general form of the equation of a circle

7. Find the center and the radius of
First group terms:

8. Add appropriate terms to complete the squares for x and for y.