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Homework Help: Weird Parabola Problem

  1. May 5, 2008 #1
    1. The problem statement, all variables and given/known data
    A parabolic communications antenna has a focus 6 feet above its vertex. Write an equation for the parabola and find the width of the antenna 9 feet from the vertex. Locate the origin strategically.

    2. Relevant equations

    y= x^2 (parent equation for parabola)

    3. The attempt at a solution
    focus = 4p.
    standard form of parabola , (x-h)^2 = 4p(y-k)^2
    4 * 6 = 24 so (x-h)^2 = 24(y-k)^2.
    It doesn't give you the origin how are you supposed to write the formula?
  2. jcsd
  3. May 5, 2008 #2


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    Science Advisor
    Homework Helper

    (h,k) is the vertex. You can put the origin anywhere you like. Why not put it at the vertex? So (h,k)=(0,0). Now what's the y coordinate 9 feet from the vertex? BTW, check your standard form for a parabola. You've got an extra square in there.
  4. May 13, 2008 #3

    I believe you're right. The equation is (x-h) = 4p(y-k)^2

    or (y-k) = 4p(x-h)^2

    So, just try x = 24y^2 and work from there ^^
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