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comp. geo with cyclic quad, related to Newton−Gauss line

Source: II Soros Olympiad 1995-96 R1 10.9 https://artofproblemsolving.com/community/c2416727_soros_olympiad_in_mathematics

June 3, 2024
geometryNewton linecyclic quadrilateral

Problem Statement

The opposite sides of a quadrilateral inscribed in a circle intersect at points KK and LL. Let FF be the midpoint of KLKL, EE and GG be the midpoints of the diagonals of the given quadrilateral. It is known that FE=aFE = a, FG=bFG = b. Calculate KLKL in terms of aa and b.b.
(It is known that the points FF, EE and GG lie on the same straight line. This is true for any quadrilateral, not necessarily inscribed. The indicated straight line is sometimes called the Newton−Gauss line. This fact can be used without proof in proving the problem, as it is known).