MathDB
czech republic,third round,2009,problem 2

Source:

February 25, 2012
geometryrectangle

Problem Statement

Rectangle ABCDABCD is inscribed in circle OO. Let the projections of a point PP on minor arc CDCD onto AB,AC,BDAB,AC,BD be K,L,MK,L,M, respectively. Prove that ∠LKM=45\angle LKM=45if and only if ABCDABCD is a square.
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