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Math Help - analytic geometry question

  1. #1
    bluebirdsfly
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    Exclamation analytic geometry question

    The perimeter of a triangle is 30, and the points (0,-5) and (0,5) are two fo the vertices. Find the equation of the ellipse of the third vertex.

    Any idea as to how to begin solving this problem...?
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  2. #2
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    Quote Originally Posted by bluebirdsfly View Post
    The perimeter of a triangle is 30, and the points (0,-5) and (0,5) are two fo the vertices. Find the equation of the ellipse of the third vertex.

    Any idea as to how to begin solving this problem...?
    An ellipse is the locus of all points which have the constant sum of distances from 2 fixed points (=focus).

    Therefore:
    1. (0, -5), (0, 5) are the focii.
    2. The sum of distances is 20. (The distance between the focii is 10!)
    3. The length of the main semiaxis must be 10.
    4. The center of the ellipse must be the origin.
    5. The length of the minor semi axis must be:  b = \sqrt{10^2-5^2} = 5 \cdot \sqrt{3}
    Attached Thumbnails Attached Thumbnails analytic geometry question-ellips_ofvertex.gif  
    Last edited by earboth; March 6th 2008 at 05:32 AM.
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