1. Learning Target #21
Equations of Circles

2. Find the distance from (h,k) to (x, y)
Standard Form for a Circle!!!

3. Write the standard form for a circle
Center (2, 5), r = 3
Center (-3, 7), r = 4
Center (-2.3, 5), r = 3.2

5. Find the center and radius
Rewrite as:

6. Write the standard equation for the circle
Center (1, 2) and a point on the circle is (4, 6)
Find the radius using distance formula!!!!
r = 5
Write the equation
(x – 1)2 + (y – 2)2 = 52
(x – 1)2 + (y – 2)2 = 25

7. Here’s some graph paper…
Graph a circle with center at (2, 1) and a radius of 3.
First make x, y axis
Plot the center
Plot a few points on the circle
Connect the dots

8. Using the previous circle… (x – 2)2 + (y – 1)2 = 9
Are these points inside, on, or outside of the circle?
(1, 1)
(1 – 2)2 + (1 – 1)2 < 9 …. inside the circle!
(3, -3)
(3 – 2)2 + (-3 – 1)2 > 9 … outside the circle!
(5, 1)
(5 – 2)2 + (1 – 1)2 = 9 … on the circle!
Plug them in the equation for x, y!!!

9. Homework Pg. 638
Pg, 638
#8-14, 16, 18-22, 26-40(e)