is an acute triangle. Through a point on , draw a circle that is tangent to at and tangent to at . Furthermore, suppose that the circumcenter of lies on the shorter arc of . Prove that the circumcircle of intersects at two points.
Solution
Clearly is the foot of the perpendicular from to , so it lies within segment . Similarly, lies within segment . Therefore must lie inside , and hence .
Now let . It is easy to see that and . Also, . Combining the above, we get
so .
Finally, let be the reflection of across . Then in the quadrilateral , we have
so must lie outside the circumcircle of . Therefore, the points and lie respectively inside and outside the circumcircle of , so the circle must intersect the circumcircle of at two points.

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