Geometry · Rectangle · Midpoints · Isosceles triangle · Congruent triangles · Angle chase

Problem 3, 2004

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NationalProof

Let \(E\) and \(F\) be the midpoints of the sides \(AD\) and \(DC\) of a rectangle \(ABCD\), and let \(G\) be the point where the segments \(AF\) and \(EC\) cross. Prove that

\[ \angle CGF = \angle FBE . \]

A B C D E F G
The two marked angles are the ones to be compared.

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Slovenian High School Mathematics Competition for Vega Awards (MaSSA), drzavno (national) round 2004, 1. letnik, category A, problem 3. Organized by DMFA Slovenije (Society of Mathematicians, Physicists and Astronomers of Slovenia). Source

National problem · Geometry · Lemma