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

**osoares10** · October 12th 2009, 03:12 PM

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

**mr fantastic** · October 12th 2009, 03:21 PM

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 $(x - h)^2 + (y-k)^2 = r^2$ .

**osoares10** · October 12th 2009, 03:28 PM

can u solve it too for me

**mr fantastic** · October 12th 2009, 03:29 PM

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.

**osoares10** · October 12th 2009, 03:35 PM

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

i cant find the numbers that go in the blank

**mr fantastic** · October 12th 2009, 03:37 PM

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.

**osoares10** · October 12th 2009, 03:38 PM

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

**mr fantastic** · October 12th 2009, 04:06 PM

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

**osoares10** · October 12th 2009, 04:37 PM

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

**osoares10** · October 12th 2009, 04:44 PM

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

**mr fantastic** · October 12th 2009, 04:46 PM

Originally Posted by osoares10

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

Yes. Well done.

**osoares10** · October 12th 2009, 04:47 PM

Originally Posted by mr fantastic

Yes. Well done.

thanks alot for the help

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