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nguyenthivananh646
2 năm trước
Cho ΔABC có 3 góc nhọn (AB<AC). Các đường cao AD, BE, CF cắt nhau tại H a/Chứng minh ΔAEB đồng dạng ΔAFC. Từ đó suy ra AF.AB = AE.AC b/Chứng minh góc AEF = góc ABC c/Vẽ DM vuông góc với AB tại M. Qua M vẽ đường thẳng song song với EF cắt AC tại N. Chứng minh DN vuông góc AC d/Gọi I là trung điểm HC. Chứng minh ΔFAC đồng dạng ΔFHB và FA.FB = FI ² - EI ²
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