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area chasing, 2 equal ratios in quadrilateral (VII Soros Olympiad R1 9.7)

Source:

July 4, 2021
geometryareas

Problem Statement

Sides ABAB and CDCD of quadrilateral ABCDABCD intersect at point EE. On the diagonalsAC AC and BDBD points MM and NN are taken, respectively, so that AM/AC=BN/BD=kAM / AC = BN / BD = k. Find the area of ​​a triangle EMNEMN if the area of ​​ABCDABCD is SS.