Cho tam giác ABC cân tại A Trên tia đối của BC lấy điểm D trên tia đối của CB lấy điểm E sao cho BD = CE Chứng minh rằng tam giác aid là tam giác cân kẻ BH vuông góc AD E thuộc AD kẻ ck vuông góc với AB K thuộc AB a chứng minh rằng BH = ck Gọi O là giao điểm của BH và ck tam giác ABC là tam giác gì Vì sao

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