Let be the circumcircle of . Let be a point on the side . The tangent to at intersects the parallel line to through at point . The segment intersects again at . Suppose are concyclic. Prove that are concurrent.
Solutions — 2
Solution 1
From the conditions, we have
Let be the intersection of and . Then we have
This implies are concyclic. It follows that
and hence and are parallel. So are collinear, and the result follows.
Solution 2
Let be any point on the extension of . From , points are concyclic.
Let be the intersection of and . From , the points are concyclic. In addition, from , points are concyclic.
By considering the radical centre of and , we find that the lines are concurrent at . The result follows.
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