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

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    Exclamation 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
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    Quote Originally Posted by osoares10 View Post
    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.
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    can u solve it too for me
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    Quote Originally Posted by osoares10 View Post
    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.
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    ok i get down to x^2+2x___+y^2-6y___=6

    i cant find the numbers that go in the blank
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    Quote Originally Posted by osoares10 View Post
    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.
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    Quote Originally Posted by mr fantastic View Post
    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
    Last edited by mr fantastic; October 12th 2009 at 04:04 PM. Reason: Merged posts
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    Quote Originally Posted by osoares10 View Post
    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
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    can some one please just do this for me, i just cant get it, i hate my teacher, please its very important
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    i think i got it, is the center -1,3 and the radius 4?
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    Quote Originally Posted by osoares10 View Post
    i think i got it, is the center -1,3 and the radius 4?
    Yes. Well done.
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    Quote Originally Posted by mr fantastic View Post
    Yes. Well done.
    thanks alot for the help
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