<Tri-2026-2353>, hint

 

<Tri-2026-2353>, general , locus

<Spain MO 1990>

 

<Tri-2026-2352>, hint

 

<Tri-2026-2352>, general, area

<Spain MO 1989>

<Tri-2026-2351>, hint

Let F on BD such that CB=CF, then ABC and CBF are similar,

CEF is equilateral.  CDF is isosceles  <FCD=<FDC=40, FDE is isosceles  FD=FE

<DFE=180-60-80=40. Hence <EDC=<EDF-<CDF=70-40=30

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