MathDB
Circumscribed quadrilateral

Source: 239 2012 J7

July 30, 2020
geometry

Problem Statement

A circumscribed quadrilateral ABCDABCD is given. It is known that ∠ACB=∠ACD\angle{ACB} = \angle{ACD}. On the angle bisector of ∠C\angle{C}, a point EE is marked such that AE⊥BDAE \bot BD. Point FF is the foot of the perpendicular line from point EE to the side BCBC. Prove that AB=BFAB = BF.
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