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hoangthuha151101
2 năm trước
Câu 1: Cho đường tròn tâm O, đường kính AB = 10cm. Trên đường tròn tâm O, lấy điểm C sao cho AC = 6cm. Kẻ CH vuông góc với AB. a) Tam giác ABC là tam giác gì? Vì sao? b) Từ O kẻ OI vuông góc với BC. Tính độ dài OI. c) Tiếp tuyến tại A của đường tròn (O) cắt tia BC tại E. Chứng minh : CE.CB = AH.AB. Câu 2: Cho đường tròn (O), và một điểm A nằm ngoài đường tròn. Từ A vẽ hai tiếp tuyến AM, AN (M, N là tiếp điếm). a) Chứng minh OA vuông góc MN b) Kẻ đường kính NOC. Chứng minh rằng MC // OA c, Tính độ dài các cạnh của tam giác AMN biết OM=3cm, OA=5cm. Giúp mình với ạ hộ mình nhé
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