Let be a cyclic quadrilateral inscribed in a circle such that . Let be a point on the segment such that . The line intersects again at . The chords and meet at . Let be the symmetric point of about . Prove that and are parallel.
Solution
Since , the points , , , are concyclic. Using the concyclic points, we obtain
This implies , and hence . Also, as , we have . Combining these, we obtain . It follows that . Now, as and are midpoints of and , we know that as desired.

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