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chuanms3203
2 năm trước
Cho tam giác cân ABC (AB = AC), các đường cao AD, BE, cắt nhau tại H. Gọi O là tâm đường tròn ngoại tiếp tam giác AHE. Chứng minh tứ giác CEHD nội tiếp Bốn điểm A, E, D, B cùng nằm trên một đường tròn.
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