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IMO 1977 — Official contest Question 1

IMO · IMO 1977 — Official contest

Question 1

Equilateral triangles $ABK,BCL,CDM,DAN$ are constructed inside the square $ABCD$. Prove that the midpoints of the four segments $KL,LM,MN,NK$ and the midpoints of the eight segments $AK,BK,BL,CL,CM,DM,DN,AN$ are the twelve vertices of a regular dodecagon.