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luulytim
![](https://blog.hocmai.vn/wp-content/uploads/2017/07/hot.gif)
![](https://blog.hocmai.vn/wp-content/uploads/2017/07/hot.gif)
trong khong gian voi he toa do de cac vuong goc Oxyz cho tu dien ABCD voi A(2;3;2) B(6;-1;-2) C(-1;-4;3) D(1;6;-5).Tim goc giua hai duong thang AB va CD.Tim toa do diem M thuoc duong thang CD sao cho tam giac ABC co chu vi nho nhat