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7 tháng 9 2015

Với a,b >0.Ta có: \(\frac{1}{a}+\frac{1}{b}\ge\frac{\left(1+1\right)^2}{a+b}=\frac{4}{a+b}\left(đpcm\right)\) 

Dấu = xảy ra khi và chỉ khi a=b

6 tháng 7 2021

chọn C 

28 tháng 7 2018

Ta có 3 trường hợp :

+ TH 1 : Nếu n > m thì a^n > a^m

+ TH 2 : Nếu n < m thì a^n < a^m

+ TH 3 : Nếu n = m thì a^n = a^m

Chúc bạn hok tốt nhé!!

27 tháng 6 2016

số đó là 16

27 tháng 6 2016

mình nghĩ vậy

7 tháng 4 2015

Với a=0 ; b=0 thì a+b=b-a=0

Với \(a\ne0;b\ne0\)thì a+b>b-a
 

Các bạn ơi giúp mình bài này với, 5 bạn trả lời đúng nhanh nhất mình sẽ v cho nha! FINAL TEST 2 I.    Find the word which has a different sound in the underlined part. 1.   A. can                          B. star                               C. bag                               D. that 2.   A. far                           B. plant                             C. plan                              D. hat 3.   A. plastic                    B....
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Các bạn ơi giúp mình bài này với, 5 bạn trả lời đúng nhanh nhất mình sẽ v cho nha!

FINAL TEST 2

I.    Find the word which has a different sound in the underlined part.

1.   A. can                          B. star                               C. bag                               D. that

2.   A. far                           B. plant                             C. plan                              D. hat

3.   A. plastic                    B. start                              C. stand                             D. land

4.   A. smart                      B. channel                         C. cancer                           D. thanks

5.   A. cart                         B. heart                             C. card                              D. animal

II.  Find one odd word for each question, and then read them aloud.

6.   A. plastic                    B. glass                             C. metal                            D. bag

7.   A. reduce                    B. repeat                           C. reuse                             D. recycle

8.   A. bottle                      B. bag                                C. bin                                D. paper

9.   A. refillable                B. reusable                        C. recycled                       D. repair

10. A. floods                     B. rubbish                         C. litter                             D. garbage

III. Choose the correct answers. of trees.

11. If we                       waste paper, we will save a lot of trees.

      A. repeat                     B. recycle                          C. rewrite                          D. remake

12. If we plant more trees in the schoolyard, the school will become a                    place.

      A. greener                   B. darker                           C. dirtier                           D. more polluted

13. "Why do you often forget to                     the lights when you go out of the classroom?"

      A. turn on                    B. turn off                         C. close                             D. shut down

14. "What can we do               air pollution?"

      A. reduce                    B. to reduce                      C. reducing                       D. to reducing

15. You can save money while shopping by only buying                  you need.

      A. what                       B. it                                   C. this                               D. that

16. "Reduce, reuse, recycle" is  said to encourage people to waste less, by using less and using things again, in order to              the environment .

      A. harm                       B. damage                         C. pollute                          D. protect

17. Please collect all the recyclable materials, and take them to the                         factory.

      A. recycle                   B. recycled                        C. recyclable                    D. recycling

18. This newspaper is made of                        paper.

      A. recycle                   B. recycled                        C. old                                D. waste

19. If we all use                       bags, we'll help the environment.

      A. new                         B. cheap                            C. reusable                        D. reduced

20. These three Rs                   . reduce, reuse, and recycle

      A. stand up                  B. stand for                       C. ask for                          D. means

21. If there is a rubbish bin in every class, the classroom will become                    .

      A. harmful                  B. lighter                           C. dirtier                           D. cleaner

22. "Don't throw rubbish into the river because you will make it                 ."

      A. greener                   B. dirty                              C. cleaner                         D. fresher

23. If we use                paper, we will save a lot of trees.

      A. fewer                      B. less                               C. more                             D. much

24. You should put the food in a reusable box                       plastic bag.

      A. by                           B. instead of                     C. because of                    D. without

25. If people turn off all electric appliances in one hour all over the world, they can save lots of                   .

      A. electric                   B. electrical                      C. electrician                    D. electricity

26. It is a good idea to                         our clothes with our friends or cousins.

      A. change                    B. swap                             C. turn                               D. send

27. Next week our class is having a discussion about finding                       ways to reuse old items before throwing them away.

      A. interested               B. surprising                     C. useless                          D. creative

28. If you have old clothes, will you give them to those                   ?

      A. needs                      B. to need                          C. for needing                   D. in need

29. My brother and I will give last year's clothes to                          instead of throwing them away.

      A. shop                        B. people                           C. charity                          D survey.

30. "Do you think we should put a                  bin in every classroom in order to keep it clean?"

      A. reusable                  B. recycled                        C. recycling                      D. recyclable

IV. Write conditional sentences from these statements.

31. We will plant more trees. The air will be fresher.                      

      If ___________________________________________ .

32. We will use fewer cars. We will reduce pollution.

      If ___________________________________________

33. We will cycle to school every day. We will keep fitter.

      If ___________________________________________

34. We will use recycled products. We will save money.

      If ___________________________________________

35. People will throw rubbish into the right bin. They will keep the environment clean.

      If ___________________________________________

36. We will turn off the tap when brushing the teeth. We will save a lot of water.

      If ___________________________________________

37. People will travel more by public transport. The harmful gases in big cities will be reduced.

      If ___________________________________________

38. We will start at 6.00. We will arrive there before noon.

      If ___________________________________________

39. The boy eats so may green apples. He will be ill.

      If ___________________________________________

40. We will use reusable bags for shopping. We will reduce waste.

      If ___________________________________________

V.     Choose the word or phrase among A, B, C or D that best fits the blank space in the following passage.

      Last month Lan's father (41)                    her to a glass factory. They visited the recycling workshop where the broken glass was smashed (42)                 small pieces, and the glass was washed with a particular detergent liquid. After that, it was dried up and mixed (43)                    some chemicals. The mixture was put into a very (44)                    temperature furnace to melt into liquid. The workers in the factory used long pipes (45)              the liquid into a variety of shapes. All the glassware looks nice. Lan was very impressed by the journey.

41. A. asked                      B. took                              C. told                               D. gave

42. A. under                      B. into                               C. in                                  D. on

43. A. in                            B. of                                  C. up                                 D. with

44. A. high                        B. strong                           C. low                               D. weak

45. A. change                    B. to make                         C. to blow                         D. to have

VI. Read the following passage, and then answer the questions below.

      Every day of the year throughout the world, about twenty million paper bags and the newspapers are screwed and thrown away. Making paper requires a lot of wood pulp and the work of millions of workers. Many countries have had plans to recycle waste paper to save money and labor. In countries where there is the cooperation of the public, paper mills recycle as much as sixty percent of waste paper. Their simple work is to take away the ink, crush it up and make it into pulp again. For every ton of recycled newsprint, twelve trees can be saved. We can insist that the more paper people save, the more trees are preserved.

46. How many paper bags and newspapers are screwed and thrown away every day?

      ___________________________________________

47. What have many countries done to save money and labor in making paper?

      ___________________________________________

48. What percentage of waste paper is recycled with the help of the public?

      ___________________________________________

49. What do the paper mills do to reuse waste paper?

      ___________________________________________

50. How many trees can be saved for every ton of recycled newsprint?

      ___________________________________________

0
5 tháng 8 2014

Thời gian đi tỉ lệ nghịch với vận tốc.

Tỉ lệ vận tốc đi và về là: 50/60 = 5/6.

Thời gian đi và về sẽ tỉ lệ nghịch với 5/6, tức là 6/5.

Gọi thời gian đi là 6 phần, thời gian về sẽ là 5 phần. Hiệu số phần là: 6 - 5 = 1 (phần).

Hiệu thời gian là 1 phần ứng với 18 phút = 0,3 giờ.

Vậy 1 phần = 0,3 giờ

=> Thời gian đi là: 0,3 x 6 = 1,8 giờ

     Thời gian về là 0,3 x 5 = 1,5 giờ.

Quãng đường AB là 1,8 x 50 = 90 km

 

10 tháng 8 2014

Thời gian đi tỉ lệ nghịch với vận tốc.

Tỉ lệ vận tốc đi và về là: 50/60 = 5/6.

Thời gian đi và về sẽ tỉ lệ nghịch với 5/6, tức là 6/5.

Gọi thời gian đi là 6 phần, thời gian về sẽ là 5 phần. Hiệu số phần là: 6 - 5 = 1 (phần).

Hiệu thời gian là 1 phần ứng với 18 phút = 0,3 giờ.

Vậy 1 phần = 0,3 giờ

=> Thời gian đi là: 0,3 x 6 = 1,8 giờ

     Thời gian về là 0,3 x 5 = 1,5 giờ.

Quãng đường AB là 1,8 x 50 = 90 km

22 tháng 10 2018

- Tên người : Lép Tôn-xtôi, Mô-rít-xơ, Mát-téc-lích, Tô-mát Ê-đi-xơn, Lê-o-na-đô-đa Vanh-xi.

- Tên địa lí: Hi-ma-lay-a, Đa-nuýp, Lốt Ăng-giơ-lét, Niu Di-lân, Công-gô.

22 tháng 10 2018

cho mk hỏi là viết phiên dịch ra tiếng việt hay viết bằng tiếng anh

Giúp mình mấy bài cuối với các bạn ơi :))Choose the correct answers.1. If that hat costs much, I           a small one.A. would have bought                                     B. will buyC. bought                                                       D. would buy2. If you              more carefully, you would not have had so many accident.A. drive                       B. drove                      C. had driven              D. has driven3. “Tom              more races if the trained...
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Giúp mình mấy bài cuối với các bạn ơi :))

Choose the correct answers.

1. If that hat costs much, I           a small one.

A. would have bought                                     B. will buy

C. bought                                                       D. would buy

2. If you              more carefully, you would not have had so many accident.

A. drive                       B. drove                      C. had driven              D. has driven

3. “Tom              more races if the trained hard.” The man said.

A. would win               B. wins                        C. would have won     D. would be winning

4. If I spoke English, my job         a lot easier.

A. was                         B. were                       C. will be                     D. would be

5. “If you feel like a chat,          .” David said to me.

A. phone to me tonight                                   B. will you phone me tonight

C. phoned me tonight                                     D. phone me tonight

6. I will lend them some money if they        me.

A. ask                          B. will ask                   C. asked                      D. had asked

7. If we had known who he was, we       him to speak at our meeting.

A. would have invited                                     B. have invited

C. will invite                                                   D. would invite

8. “If you             too much junk food, you would be a lot fitter.” Mother said.

A. ate                           B. didn’t eat                C. didn’t ate                D. had eaten

9. If I              enough money. I would buy a house.

A. had                          B. had had                   C. will have                 D. have

2
10 tháng 1 2022

1. If that hat costs much, I           a small one.

A. would have bought                                     B. will buy

C. bought                                                       D. would buy

2. If you              more carefully, you would not have had so many accident.

A. drive                       B. drove                      C. had driven              D. has driven

3. “Tom              more races if the trained hard.” The man said.

A. would win               B. wins                        C. would have won     D. would be winning

4. If I spoke English, my job         a lot easier.

A. was                         B. were                       C. will be                     D. would be

5. “If you feel like a chat,          .” David said to me.

A. phone to me tonight                                   B. will you phone me tonight

C. phoned me tonight                                     D. phone me tonight

6. I will lend them some money if they        me.

A. ask                          B. will ask                   C. asked                      D. had asked

7. If we had known who he was, we       him to speak at our meeting.

A. would have invited                                     B. have invited

C. will invite                                                   D. would invite

8. “If you             too much junk food, you would be a lot fitter.” Mother said.

A. ate                           B. didn’t eat                C. didn’t ate                D. had eaten

9. If I              enough money. I would buy a house.

A. had                          B. had had                   C. will have                 D. have

10 tháng 1 2022

1. If that hat costs much, I           a small one.

A. would have bought                                     B. will buy

C. bought                                                       D. would buy

2. If you              more carefully, you would not have had so many accident.

A. drive                       B. drove                      C. had driven              D. has driven

3. “Tom              more races if the trained hard.” The man said.

A. would win               B. wins                        C. would have won     D. would be winning

4. If I spoke English, my job         a lot easier.

A. was                         B. were                       C. will be                     D. would be

5. “If you feel like a chat,          .” David said to me.

A. phone to me tonight                                   B. will you phone me tonight

C. phoned me tonight                                     D. phone me tonight

6. I will lend them some money if they        me.

A. ask                          B. will ask                   C. asked                      D. had asked

7. If we had known who he was, we       him to speak at our meeting.

A. would have invited                                     B. have invited

C. will invite                                                   D. would invite

8. “If you             too much junk food, you would be a lot fitter.” Mother said.

A. ate                           B. didn’t eat                C. didn’t ate                D. had eaten

9. If I              enough money. I would buy a house.

A. had                          B. had had                   C. will have                 D. have