In acute , . Let be the point on the side such that . Let be the midpoint of . The tangents at and to the circumcircle of intersect at point . The line intersects the side at . Prove that are concyclic.
Solutions — 2
Solution 1
Suppose meets () again at . Applying Pascal's theorem to the points , we know that , and are collinear. Thus, passes through . Now, since
the points are concyclic.

Solution 2
We provide another proof without using Pascal's theorem as follows. Again, the main task is to prove are collinear. We define as the intersection point of and . It suffices to prove are collinear. Suppose meets () again at , and meets () again at .
Firstly, since , the powers of with respect to () and () are the same. Thus, lies on the radical axis of these circles.
Secondly, as , we have . Also, as , we have . Therefore, are collinear, and . Since , we have . From this, it follows that , and hence lies on the radical axis of () and ().
Thirdly, it is clear that lies on the radical axis of () and (). It follows that are collinear as desired.