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A convex quadrilateral ABCD

Source: Own (Oliforum contest 2009/round 2/2)

October 18, 2009
trigonometrygeometrygeometric transformationreflectionfunctioncircumcircleangle bisector

Problem Statement

Let a convex quadrilateral ABCD ABCD fixed such that AB \equal{} BC, \angle ABC \equal{} 80, \angle CDA \equal{} 50. Define E E the midpoint of AC AC; show that \angle CDE \equal{} \angle BDA (Paolo Leonetti)
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