Martin Josefsson, The area of a bicentric quadrilateral,
Forum Geometricorum, 11 (2011) 155--164.

Abstract.   We review and prove a total of nine different formulas for the area of a bicentric quadrilateral. Our main result is that this area is given by K= (m^2-n^2)kl/(k^2-l^2) where m, n are the bimedians and k, l the tangency chords.

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