- tren duong thang xx' lay diem O . Tren cung 1 nua mat phang bo la tia xx'. Ve 3 tia Ot, Oy, Oz sao cho goc x'Oy =40 do, goc xOt=97 do, goc xOz = 54 do
a, Chung to tia Ot nam giua hai tia Oy va Oz
b, Chung to tia Ot la tia phan giac cua goc yOz
Giai Day Du , Minh tick cho