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tinbrvt159
2 năm trước
Cho tam giác ABC có 3 góc nhọn, kẻ hai đường cao BD và CE cắt nhau tại H. 1. Chứng minh bốn điểm A, E, H, D cùng thuộc một đường tròn . xác định tâm I của đường tròn đó. 2. Chứng minh AH vuông góc BC. 3. Cho góc A = 600 , AB = 6cm. tính BD. 4. Gọi O là trung điểm của BC. Chứng minh OD là tiếp tuyến của đường tròn (I) CÂu 4 ạ
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