hlepppppppppppppppppp Bài 1: Cho tam giác ABC cân tại A. Gọi I là trung điểm của cạnh BC. Chứng minh rằng: a) AI là tia phân giác của góc A. b) AI vuông góc với BC. Bài 2. Cho góc xOy có số đo 120 o  điểm A thuộc tia phân giác của góc đó. Kẻ AB vuông góc với Ox, kẻ AC vuông góc với Oy. Tam giác ABC là tam giác gì ? Vì sao? Bài 3.Cho tam giác ABC nhọn. Trên tia đối của tia AB lấy điểm D sao cho AD = AC; trên tia đối của tia AC lấy điểm E sao cho AE = AB. a) Chứng minh: BC = DE. b) Tam giác ACD và tam giác ABE là tam giác gì? c) Gọi M là trung điểm của BE. Chứng minh AM vuông góc với BE. mik sẽ hậu tạ 5 sao giúp mik với đến ngày mai là mik hết hạn để nộp

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