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quadrilateral PEFG is maximum

Source: China TST 1988, problem 6

June 27, 2005
geometrytrapezoidgeometry unsolved

Problem Statement

Let ABCDABCD be a trapezium AB//CD,AB // CD, MM and NN are fixed points on AB,AB, PP is a variable point on CDCD. E=DNAPE = DN \cap AP, F=DNMCF = DN \cap MC, G=MCPBG = MC \cap PB, DP=λCDDP = \lambda \cdot CD. Find the value of λ\lambda for which the area of quadrilateral PEFGPEFG is maximum.