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OMM 2021 Problem 4

    Let ABCABC be an acutangle scalene triangle with ∠BAC=60∘\angle BAC = 60^{\circ} and orthocenter HH . Let ωb\omega_b be the circumference passing through HH and tangent to ABAB at BB , and ωc\omega_c the circumference passing through HH and tangent to ACAC at CC .

    • Prove that ωb\omega_b and ωc\omega_c only have HH as common point.
    • Prove that the line passing through HH and the circumcenter OO of triangle ABCABC is a common tangent to ωb\omega_b and ωc\omega_c .

    Note: The orthocenter of a triangle is the intersection point of the three altitudes, whereas the circumcenter of a triangle is the center of the circumference passing through it's three vertices.

    Dataset text AI-MO AoPS. Quoted with source.

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