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trinhtunglpa
![](https://blog.hocmai.vn/wp-content/uploads/2017/07/hot.gif)
![](https://blog.hocmai.vn/wp-content/uploads/2017/07/hot.gif)
tu mot diem A nam ben ngoai duong tron (O) ke cac tiep tuyen AB,AC voi duong tron (B<C la cac tiep diem).Qua diem M thuoc cung nho BC ke tiep tuyen voi duong tron (O), no cat cac tiep tuyen AB va AC theo thu tu o D va E . chung minh rang chu vi tam giac ADE bang 2AB