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Math Help - Circle Graph

  1. #1
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    Circle Graph

    What would this graph look like: 3y^2 + 3x^2 + 12y=0.

    I know that it is a circle but how do I work out the center and the radius of it? Thanks in advance.
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  2. #2
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by Air View Post
    What would this graph look like: 3y^2 + 3x^2 + 12y=0.

    I know that it is a circle but how do I work out the center and the radius of it? Thanks in advance.
    divide through by 3 and group the y's. you will get:

    x^2 + (y^2 + 4y) = 0

    now complete the square for the y's and get your equation in the form: (x - h)^2 + (y - k)^2 = r^2 (we already know h = 0)

    the center is (h,k) and the radius is r
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  3. #3
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    Quote Originally Posted by Air View Post
    What would this graph look like: 3y^2 + 3x^2 + 12y=0.

    I know that it is a circle but how do I work out the center and the radius of it? Thanks in advance.
    You should not have been given this problem without a refresher on "Completing the Square". complete the Square on the 'y's and you will be done.

    3x^2 + 3y^2 + 12y = 0

    x^2 + y^2 + 4y = 0

    x^2 + (y^2 + 4y + something) = something

    4/2 = 2
    2^2 = 4 = something

    x^2 + (y^2 + 4y + 4) = 4

    I'll leave you the last step.
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