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Another simple one on quads

Source: Indian RMO 1992 Problem 6

October 15, 2005
geometry

Problem Statement

ABCDABCD is a quadrilateral and P,QP,Q are the midpoints of CD,AB,AP,DQCD, AB, AP, DQ meet at XX and BP,CQBP, CQ meet at YY. Prove that A[ADX]+A[BCY]=A[PXOY]A[ADX]+A[BCY] = A[PXOY].