MathDB
6 points in a parallelogram, two equal segments

Source: JBMO Shortlist 2005

October 13, 2017
geometryparallelogramJBMO

Problem Statement

Let ABCDABCD be a parallelogram. P(CD),Q(AB)P \in (CD), Q \in (AB), M=APDQM= AP \cap DQ, N=BPCQN=BP \cap CQ, K=MNAD K=MN \cap AD, L=MNBCL= MN \cap BC. Prove that BL=DKBL=DK.