Cho tam giác đều ABC nội tiếp đường tròn tâm O và M là một điểm thay đỏi trên đường tròn.Chứng minh rằng MA^2+MB^2+MC^2 không đổi

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Ex 1. Choose the suitable prepositions in brackets 1. Ba and Tam usually go fishing........................the weekends. (on, in, from, at) 2. The students will visit the capital.........................the summer. (on, in, at, of) 3. They heard a very strange noise............................midnight. (on, in, at, out) 4. Our little brother took a long nap from 1p.m.......4p.m. (till, up, between, at) 5. She talked........................an hour to persuade her parents. (in, for, at, up to) 6. They have learned English............many years. (since, for, in, from) 7. The boys often go skiing..........................the winter. (in, at, on, for) 8. I’ve studied French................................3 months. (for, since, in) 9. I arrived.......................the bus stop at 4 in the afternoon. (in, at, on, to) 10. We have lived in Hanoi............................4 years. (in, since, for, at) 11. She was born................................16th January. (in, of, at, on) 12. I’ve studied French................................last week. (for, since, in) 13. arrived at the bus stop at 4 ........................ the afternoon. (in, at, on, to) 14. What did she do ......................the weekend? (on, in, to, for) Ex 2. Rewrite sentences by using SO: 1. They could help you because they were not here. → …………………………........................................................................................ 2. I can’t go out because it’s raining. → …………………………........................................................................................ 3. This book is interesting enough for me to read twice. → …………………………....................................................................................... 4. There was fog. Their flight was delayed → …………………………........................................................................................ III. Join each pair of sentences using SO ….THAT 1. The holidays were very cheap. They booked one immediately → …………………………...................................................................................... 2. The plane was very late. They got to bed at three in the morning → …………………………..................................................................................... 3. The way to the beach was very long. It took them an hour to walk there → ………………………….................................................................................... 4. The beach was very crowded. There was hardly room to sit down → …………………………................................................................................... IV. Rewrite sentences 1. The water was very dirty. We decided not to go swimming. → The water was so ………………………….................................................... 2. She speaks English very well. You would thing it was her native language. → She speaks English so…………………………............................................. 3. The road is so narrow that it’s difficult for two cars to pass each other. → It is………………………….......................................................................... 4. The weather was so warm that I didn’t need a coat → It was…………………………......................................................................