Subcontests
(3)concyclic points wanted, related to circumcircle, midpoint, perpendicular
Consider an acute triangle ABC with AB>AC inscribed in a circle of center O. From the midpoint D of side BC we draw line (ℓ) perpendicular to side AB that intersects it at point E. If line AO intersects line (ℓ) at point Z, prove that points A,Z,D,C are concyclic.