Question

What are the center and radius of the circle with equation (x+2)^2+(y-9)^2=16

Answer 1

Compare your "(x+2)^2+(y-9)^2=16" to the standard equation of a circle with center at (h,k) and radius r:\[(x-h)^2+(y-k)^2=r^2\]

Can you read off the values of h, k and r through this comparison?

Answer 2

Compare (y-9) to (y-k). This is the easiest comparison. What is the value of k?

Answer 3

9

Answer 4

Yes, and so the center of your circle is (h, 9).
What is the x-coordinate of the center? Do another comparison. Be very careful with your signs + and - .

Answer 5

2

Answer 6

No. Try again. Compare (x-k) to (x+2). Are the signs the same?

Answer 7

-2

Answer 8

Look at the right side of your equation: 16. thios represents r^2. What is r?

Answer 9

So, the coordinates of the center of your circle are ( ? , ? )

Answer 10

(-2,9) Radius 4

Answer 11

Perfect. Review our discussion. Then you'll be done.