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precal help

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Find a Parabola with Vertex (3,1) Focus (4,1)

Find the vertex of 4y^2+4y-16x+13=0

Find the center of an ellipse 9x^2+4y^2-36x-24y-36=0

Find an ellipse with minor axis of 8 and vertices at (-9,3),(7,3)

  • precal help - ,

    In all of these problems complete the square, then look at standard form of conic section.
    For example to find the center of the ellipse
    Find the center of an ellipse 9x^2+4y^2-36x-24y-36=0
    9 x^2 -36 x -36 = -4 y^2 + 24 y

    (-9/4) x^2 + 9 x + 9 = y^2 -6 y
    (-9/4) x^2 + 9 x + 18 = y^2 -6 y + 9
    (-9/4) x^2 + 9 x + 18 = (y-3)^2
    x^2 - 4 x - 8 = (-4/9) (y-3)^2
    x^2 - 4 x = (-4/9) (y-3)^2 + 8

    x^2 - 4 x + 2 = (-4/9) (y-3)^2 + 10
    (x-2)^2 + (4/9) (y-3)^2 = 10
    You can see right now that center is at (2,3)
    (x-2)^2/10 + (y-3)^2/(90/4) = 1

  • error - ,

    x^2 - 4 x = (-4/9) (y-3)^2 + 8

    x^2 - 4 x + 4 = (-4/9) (y-3)^2 + 12
    (x-2)^2 + (4/9) (y-3)^2 = 12
    You can see right now that center is at (2,3)
    (x-2)^2/12 + (y-3)^2/(27) = 1

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