Let the circumcircle of triangle be , the incenter be , and the -excenter be . Let be the reflection of over , and let be the intersection of and . If the circumcircle of meets at , and lies on such that , prove that: the circumcircle of is tangent to line .
Solution
(∠ denotes directed angles.)

Let , be the midpoints of , respectively, let be the reflection of over , and let be the foot of the perpendicular from to . It is well known that , and also , so and are homothetic, hence since is the reflection of over , we know . Let be the circumcenter of ; from we obtain that are concyclic. From and the Shooting Lemma (雞爪定理), we know , that is, is tangent to . Let be the intersection of and ; from and the Shooting Lemma, we know , so is tangent to . From we obtain that are collinear. Also , so , hence is tangent to .
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