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daothuyvan67
2 năm trước
Từ điểm A ở ngoài đường tròn (O; R) là hai tiếp tuyến AB, AC (B, C là hai tiếp điểm). Gọi H là giao điểm của OA và BC. a, CM: \(OA ⊥ BC\) và tính tích \(OH.OA\) theo \(R\) b, Kẻ đường kính BD của đường tròn (O). CM: CD//OA c, Gọi E là hình chiếu của C trên BD, K là giao điểm của AD và CE. CM: K là trung điểm của CE
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