The circles O and O_{1} intersect at A and B (see the figure above),
CD is the common external tangent, CA intersects circle O_{1} at E,
DA intersects circle O at F, FC and
ED intersect at G. Prove that the points B,C,G,E are concyclic,
similarly B,D,G,F are concyclic.
Dynamic Geometry of Problem 899
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