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Homework Help: Quetion to find the equation of a parabola i want check

  1. Apr 21, 2010 #1
    Hi all

    Use the definition of a parabola and the distance formula to find the equation of a parabola with

    a ) directix x = -4 and focus (2,2 )
    B ) directix x = 2 and focus (6,-4 )

    my answer :


  2. jcsd
  3. Apr 21, 2010 #2


    Staff: Mentor

    Your work for a) is not consistent with the requirements above. In your work for a, you have y = -4. Which is it?

    For b), because the directrix is x = 2, the parabola has to open to the left or right. Yours opens upward, which is wrong.

    Also, you don't draw the directrix for either parabola in your graph. The vertex of the parabola is halfway between the directrix and focus, so you can use the directrix and focus to figure out where the vertex is.

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