olymmath

IGO 2022 I1

  • Intermediate

Given is a circle ω\omega and a line ℓ\ell tangent to ω\omega at YY . Point XX lies on ℓ\ell to the left of YY . The tangent to ω\omega , perpendicular to ℓ\ell meets ℓ\ell at AA and touches ω\omega at DD . Let BB a point on ℓ\ell , to the right of YY , such that AX=BYAX=BY . The tangent from BB to ω\omega touches the circle at CC . Prove that ∠XDA=∠YDC\angle XDA= \angle YDC .

Note: This is not the official wording (it was just a diagram without any description).

Dataset text AI-MO AoPS. Quoted with source.

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