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phonghailoc
2 năm trước
Mọi người giúp em ạ Cho (O) đường kính AB, trên tiếp tuyến tại A của (O) lấy C sao cho AB = AC. BC cắt (O) tại D. Vẽ AH vuông góc CO tại H. AH cắt BC tại E. BH cắt AC tại F. a) Chứng minh rắng: HD vuông góc HB b) Chứng minh rắng: OC, EF, AD đồng qui.
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