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In cyclic quadrilateral ABCD,
let E, F, G, H be the orthocenters of triangles BCD, CDA, DAB, ABC, respectively. Prove that EFGH is cyclic.
So far, found that if E is orthocenter of BCD and F is orthocenter of CDA, then EF||AB.
Required, but never shown
4 years, 6 months ago