Source

simelo-math / IMO / 2007 / imo2k7p2.euk

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A B C D parallelogram

locus E(t = 0.1 to 0.9 step 20)
  F = barycenter(C, t, D, 1 - t)
  l = line(A, F)
  G = intersection(l, line(B, C))
  put center(circle(C, F, G))
end