olymmath

JBMO-SL 2018 G2

    Let ABCA B C be a right angled triangle with ∠A=90∘\angle A=90^{\circ} and ADA D its altitude. We draw parallel lines from DD to the vertical sides of the triangle and we call E,ZE, Z their points of intersection with ABA B and ACA C respectively. The parallel line from CC to EZE Z intersects the line ABA B at the point NN Let A′A^{\prime} be the symmetric of AA with respect to the line EZE Z and I,KI, K the projections of A′A^{\prime} onto ABA B and ACA C respectively. If TT is the point of intersection of the lines IKI K and DED E, prove that ∠NA′T=∠ADT\angle N A^{\prime} T=\angle A D T.

    Dataset text NuminaMath olympiads. Quoted with source.

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