Đáp án:
`A=2x^2-4x+7`
`=2(x^2-2x+7/2)`
`=2(x^2-2x+1-1+7/2)`
`=2[(x-1)^2+5/2]`
`=2(x-1)^2+5`
Ta cóa: `2(x-1)^2>=0`
`-> 2(x-1)^2+5>=5`
Dấu "=" xảy ra `<=> 2(x-1)^2=0`
`-> x-1=0`
`-> x=1`
Vậy `A_(min)=5 <=> x=1`
Giải thích các bước giải:
`A=2(x^2-2x+7/2)`
`A=2(x-1)^2+5 \ge 5 ∀ x`
`A_{min}=5`
Dấu `=` xảy ra khi `x-1=0⇔x=1`
Vậy `A_{min}=5` khi `x=1`
I. Circle the most suitable word or phrase to complete the sentences below. 1. You must. A. keep silent B. to keep silent 2. Shall we go.. .bicycle? A. with 3. What shall we .......this evening? A. does B. to do 4. Can I .....your book? A. borrows II. Find the word which has a different sound in the part underlined. 9. A. city 10. A. advice 9. a. home 10. a. lunch 11. a. cat 12. a. books 13. a. cook 14. He listens.......music every night. a. for b. of 15. There is a big yard...front......the house. a. at b. on c. in 16. There ..in class. C. keeping silent В. on D. keeps silent C. by C. doing C. to borrow D. at D. do B. borrow D. borrowing B. cathedral C. central D. cinema B. price C. nice D. police b. go b. up b. breakfast b. shops b. clean C. sport c. number c. read c. hats c. celebrate c. to d. about d. old d. literature d. teacher d. tables d. candy d. to ... a cinema and two shops near my house. c. is a. have b. has 17. My new school a. has d. are ... many trees and rock chairs on the yard. b. does 18. My house is not far c.have d. is my school. a. near b. from c. in 19. My mother buys me a. the 20. Mrs. Ann d. on ..uniform on the first day of new school year. d. these b. an c. a ..a long beautiful dress now. a. wears b. wearing c. is wearing d. wear 21. You'd better .. to school on time. a. goes b. go 22. Nick a. travel 23. Would you like to drink tea? a. no, thanks 24. We (not/ go) 25. (He/have).... 26. Mr. Ba (not work)..... 27. Students must (clean). 28. Mike shouldn't (stay).... III. Read the passage .Then answer the questions. c. to go to Da Nang city by train every year. b. traveling c. to travel d. travels b. no, sorry d. of course C. no, not now To school on Saturday. ..lunch at school? ..here. He (work).... ..in a factory on Le Loi street. .the classroom everyday. up late. lo, My name is Linh. I live in the country side with my father, my mother and my brother Minh. My house is next to small market. In my neighborhood, there is a temple, a lake and a store. There are many trees and flowers around my house. My father is a farmer. He works on the farm. My brother is a student at Tran Quang Dieu School. And my mother does the housework at home. 1. Where does Linh live? 2. How many people are there in her family? 3. Is her house next to a book store? 4. What are there around her house? 5. Does her brother study at Tran Quang Dieu School? IV. Complete the sentences with the correct form of the adjectives in the brackets. 1. Mount Everest is the 2. Ha Long Bay is.. 3. Traveling by bus i.. ..mountain in the world. (high) than Phu Quoc Island. (famous) than by taxi. (cheap) than Mekong River (long)
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Giải giúp mik bài 5 vẽ hộ mik hình nx nha mơn mọi người nhiều
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