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huyson7578
2 năm trước
Cho hai đường tròn (O) và (O1) ở ngoài nhau . Đường nối tâm OO1 cắt các đường tròn (O) và (O1) tại các điểm A , B , C , D theo thứ tự trên đường thẳng . Kẻ tiếp tuyến tuyến chung ngoài EF ( E thuộc (O) , F thuộc (O1) ) . Gọi M là giao điểm của AE và DF , N là giao điểm của EB và FC . Chứng minh rằng : a) Tứ giác MENF là hình chữ nhật . b) MN vuông AD c) ME . MA = MF . MD
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