cho tam giac ABC B=60 tren tia doi BC lay diem E sao cho BE=BA . qua B ve 1 duong thang song song AE cat AC o F a] chung minh BE la phan giac cua goc ABC b] Qua A ve mot duong thang vuong goc BF cat BC tai D .Chung minh tam giac ABC deu c] goi Ax la tia doi cua AB . Chung minh goc CAx =goc CDF d] chung minh AF=FC