quadrilateral ....
Source: Iran(2003)
March 13, 2004
geometrygeometry solved
Problem Statement
assume ABCD a convex quadrilatral. P and Q are on BC and DC respectively such that angle BAP= angle DAQ .prove that [ADQ]=[ABP]
([ABC] means its area ) iff the line which crosses through the orthocenters of these traingles , is perpendicular to AC.