Cho (O) đường kính AB, trên cùng một nửa đường tròn (o) lấy 2 điểm G và E (theo thứ tự A, G, E, B) sao cho tia EG cắt tia BA tại D. Đường thẳng vuông góc với BD tại D cắt BE tại C, đường thẳng CA cắt đường tròn (O) tại điểm thứ hai là F. CMR: a, D,F,B,C cùng ∈ 1 đường tròn b,BF=BG c,DA/BA=( DG*DE)/(BE*BC)

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