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2 năm trước
Cho tam giácABC vuông cân tại A , gọi O là trung điểm của BC . Trên cạnh AB AC , lần lượt lấy các điểm E F, tương ứng sao cho góc EOF = 45 độ d) Gọi D là điểm đối xứng của A qua O . Khi E F, thay đổi trên cạnh AB AC , sao cho góc EOF = 45 . Chứng minh rằng: Đường thẳng đi qua E song song với DF luôn đi qua một điểm cố định.
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