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cho tam giác nhọn ABC có các đường cao AD,BE và CF đồng quy tại H chứng minh: a)tam giác AEF đồng dạng với yam giác ABC;b) H là giao điểm các đường phân giác của tam giác DEF;c)BH.BE+CH.CF = BC bình phương
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Exercise 7: Change into passive or active : 1. People speak English here. => 2. They don't sell stamps in bookshops. => 3. Nguyen Du wrote Kieu’s story. => 4. The teacher is going to tell us a story. => 5. Someone was cleaning the classroom when I came => 6. This factory is producing more and more pollution. => 7. Were the letters sent by Tom? => 8. No one has signed the check. => 9. Nobody believes his story. => 10. Do they teach English in your school? => 11. This store was opened by Mr John in 1990. => 12. The lessons are being written by the students. => 13. Someone broke into my room and took away some pictures. => 14. She will send him a gift on his birthday. => 15. They gave me that bicycle last week. => 16. We know that English is an international language. => 17. People believed that the earth stood still. => 18. They declared that he has died a natural death. => 19. It is believed that 13 is an unhappy number. => 20. The owner of the house was said to have gone abroad. => 21. It is said that she works 16 hours a day. => 22. They think that the prisoner escaped by climbing over a wall. => 23. A nurse bandaged his arm.

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