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kun_ny
![](https://blog.hocmai.vn/wp-content/uploads/2017/07/hot.gif)
![](https://blog.hocmai.vn/wp-content/uploads/2017/07/hot.gif)
Cho tam giac ABC can tai A. Lay diem D nam giua~ B va C. Qua D lan luot ve hai duong thang? song song voi AC cat AB tai E, song song voi AB cat' AC tai F
- C/m DE + DF =AB
- Goi I la diem doi xung cua D qua EF . C/m tu giac' AEFI la hinh thang can
- C/m I thuoc duong tron ngoai tiep tam giac ABC:-SS:-SS