olymmath

NZ-NZMO 2025 Problem 7

    Let ABCABC be a triangle and let DD be a point inside the triangle ABCABC such that ADAD bisects ∠BAC\angle BAC. Let line BDBD meet side ACAC at EE. Let line CDCD meet side ABAB at FF. Let TT be the intersection of the (internal) angle bisectors of ∠AED\angle AED and ∠AFD\angle AFD. Prove that if TT lies on segment ADAD, then triangle ABCABC is isosceles.

    Dataset text NuminaMath olympiads. Quoted with source.

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