Co hai goc xOt va yOt ke bu -> xOt + yOt = 180 -> 50 + yOt = 180 -> yOt = 180 - 50 = 130 do
Co tia Oz nam giua 2 tia Oy va Ot -> yOz + zOt = yOt = 130 (chung minh tren) -> 80 + zOt = 130 -> zOt = 130 - 80 = 50 do
Co tia Ot nam giua 2 tia Oz va Ox, lai co zOt = xOt (cung bang 50 do) -> Ot la phan giac goc xOz