Tìm x biết x²-4⋮x-1

IV.Change this sentences into passive 1.Somebody has cleaned the room. 2.They have postponed meeting. 3.Sombody is using computer at the moment. 4.I didn't realise that somebody was recording our conversation. 5.Getting to the stadium,we found that they have cancelled the game. 6.They are building a new ring road round the city. 7.They have built a new hospital near the airport.

a.Cho tia tới theo phương nằm ngang được tia phản xạ vuông góc chiều từ trên xuống.Xác định số đo của góc tạo bởi gương phẳng với phương nằm ngang