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Math Help - Putnam Problem of the Day (2)

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    Putnam Problem of the Day (2)

    Let be a convex quadrilateral such that diagonals and intersect at right angles , and let be their intersection . Prove that the reflections of across are concyclic



    Hint :

    Spoiler:
    Consider the quadrilateral constructed by the feet of the perpendicular of  E to the sides of  ABCD .



    Moderator edit: Approved Challenge question.
    Last edited by simplependulum; May 31st 2010 at 09:00 PM. Reason: Approved.
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