Let be the midpoint of the side of an acute , and let be the foot of perpendicular from to . The circumcircle of intersects the side again at . Suppose is a point on the segment such that . Prove that is the midpoint of .
Solution
Let be the foot of perpendicular from to . It follows from that , , , are concyclic. Considering the power of , we find that
Since , we have . Note that is the perpendicular bisector of . Therefore, . As , it follows from the intercept theorem that is the midpoint of .

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