# Thread: general equations for circles, how to find the radius and center

1. ## general equations for circles, how to find the radius and center

hi this is my first thread, im doing corrections for a math test i bombed

i have the equation x^2+y^2+2x-6y-6=0

can someone help me find the center and the radius

2. Originally Posted by osoares10
hi this is my first thread, im doing corrections for a math test i bombed

i have the equation x^2+y^2+2x-6y-6=0

can someone help me find the center and the radius
Complete the square in x-terms and y-terms and re-arrange to get the form $(x - h)^2 + (y-k)^2 = r^2$.

3. can u solve it too for me

4. Originally Posted by osoares10
can u solve it too for me
No. I have told you what to do. Make an attempt. Show all your working. Say where you get stuck.

5. ok i get down to x^2+2x___+y^2-6y___=6

i cant find the numbers that go in the blank

6. Originally Posted by osoares10
ok i get down to x^2+2x___+y^2-6y___=6

i cant find the numbers that go in the blank
The x-terms can be written (x + 1)^2 - 1.

You do the y-terms. It looks like you need to thoroughly review how to complete the square.

7. Originally Posted by mr fantastic
The x-terms can be written (x + 1)^2 - 1.

You do the y-terms. It looks like you need to thoroughly review how to complete the square.
isnt 1^2 = 1?

please i really need to know this if i see it i will, but i can only find examples with a perfect square, i just cant figure it out

8. Originally Posted by osoares10
isnt 1^2 = 1?

please i really need to know this if i see it i will, but i can only find examples with a perfect square, i just cant figure it out
Read this: Completing the Square: Solving Quadratic Equations

9. can some one please just do this for me, i just cant get it, i hate my teacher, please its very important

10. i think i got it, is the center -1,3 and the radius 4?

11. Originally Posted by osoares10
i think i got it, is the center -1,3 and the radius 4?
Yes. Well done.

12. Originally Posted by mr fantastic
Yes. Well done.
thanks alot for the help