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phuien05
2 năm trước
cho tam giác ABC có AB<AC và AD là phân giác. Trên nửa mp bờ BC không chứa A vẽ tia Cx sao cho góc BCx=góc BAD,Cx cắt tia AD ở E. Kẻ EH vuông góc với AC tại H. Lấy điểm I đối xứng với C qua EH. Chứng minh :a)∆DAB~∆DCE ,b)∆ECB là tam giác cân, c)AD.AD=AB.AC-BD.DC,d) I,B đối xứng nhau qua AE
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