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 to the sides of .
Moderator edit: Approved Challenge question.
Last edited by simplependulum; May 31st 2010 at 08:00 PM.
Reason: Approved.