In cyclic quadrilateral ABCD, let E, F, G, H be the orthocenters of triangles BCD, CDA, DAB, ABC, respectively. Prove that EFGH is cyclic.
Progress
So far, found that if E is orthocenter of BCD and F is orthocenter of CDA, then EF||AB.
2026-03-25 20:15:58.1774469758
Problem about cyclic quadrilaterals
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