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Math Help - Finding the equation of a parabola

  1. #1
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    Finding the equation of a parabola

    I need to find the equation of a central parabola with one focus (4,0), directrix x = 1 and eccentricity = 2

    I know the vertex form of a parabola is y = a(x-h)^2+k
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  2. #2
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    I thought that the eccentricity of a parabola was always 1. Perhaps you can clarify a bit.

    In any case, the vertex (h,k) lies halfway between the focus and directrix. So, the vertex is (5/2,0). Thus, h=5/3, k=0.

    My guess for the rest is a=(4)(2)=8. But I'm not certain about this. Perhaps someone else can clear up the definition of eccentricity being used.
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