If h and k are both zero, the center of the circle will be the origin.

For the circle graphed, the center is at (0, 0) and the radius is 5 units.

Using this information, identify the following parameters. Click on the blank to see the correct answer.

h = Interactive button. Assistance may be required. __________    0

k = Interactive button. Assistance may be required. __________    0

r = Interactive button. Assistance may be required. __________    5

What do points B, C, D, E, F, G, H, and J have in common? Interactive button. Assistance may be required. ______________________________ They are all 5 units from point A, the center.

Let’s look at that statement algebraically for point G (-3, -4):

In this circle, h and k both equal 0, so we can put the x- and y-coordinates of G into the equation to “prove” it lies on the circle.

Can you prove, using the same method, that point D is on the circle?