3xy + x - 6y = 21

(3xy - 6y) + x = 21

3y(x - 2) + x - 2 = 21 - 2

(x - 2)(3y + 1) = 19

*) x - 2 = -19; 3y + 1 = -1

+) 3y + 1 = -1

3y = -1 - 1

3y = -2

y = -2/3 (loại)

*) x - 2 = -1; 3y + 1 = -19

+) 3y + 1 = -19

3y = -19 - 1

3y = -20

y = -20/3 (loại)

*) x - 2 = 1; 3y + 1 = 19

+) x - 2 = 1

x = 1 + 2

x = 3 (nhận)

+) 3y + 1 = 19

3y = 19 - 1

3y = 18

y = 18 : 3

y = 6 (nhận)

*) x - 2 = 19; 3y + 1 = 1

+) x - 2 = 19

x = 19 + 2

x = 21 (nhận)

+) 3y + 1 = 1

3y = 1 - 1

3y = 0

y = 0 (nhận)

Vậy ta được các cặp giá trị (x; y) thỏa mãn yêu cầu đề bài:

(3; 6); (21; 0)

3^1994 + 3^1993 - 3^1992=3^1992(3^2 + 3 -1)= 3^1992.11

9^9996=(3^2)^9996=3^19992.

=> 3^1994+3^1993-3^1992 < 9^9996

chúc bạn học tốt nhé

Mình like r nha, mh cũng chẳng cần tick đou, nhg tốt nhất lần sau bạn k đăng nhg nội dung k liên quan lên diễn đàn nha, sẽ trôi mấy câu hỏi khác. Ngoài ra, mấy câu này sớm muộn cũng bị ẩn với đăng nhiều lần nhg câu k liên quan như vậy có thể bị khoá acc đó

III. Complete the sentences by filling in the gap with must and a verb

1. All visitors …must report……..to reception. You ……must come…….and stay with us one week

2. Candidates ………must answer…..…….two questions from each paper

3. I ……must go….to the bank and get some money. I …must admit….….you look absolutely great

4. We ………must get…..together soon for lunch. We ……must meet.……for lunch soon.

5. I ……must say……., I wasn’t looking forward to it. I ….must do…….some ironing tonight.

6. You ………must be….…. hungry after all that walking.

IX. Find ONE mistake in each of the following sentences and correct it

1. He is intelligenter than I am…………more intellignet…………

2. She is tallest girl in the village…………the tallest…………

3. Is there a lot of food in the fridge? _ No, there isn’t some.……any…………

4. We must not forgets your birthday.…………forget…………

5. My house is beautiful than hers.……………more beautiful………

6. Where can I find Mr. Brown? _ He is at the sixth floor. ……on..…………

7. Thank you very much. Where is the lift? ____ He’s over there.…It's…………

8. Do you like your place new? _ Yes, we do. It’s a big house.………new place………

VIII. Put the words in the correct order to make the right sentences.

1. Dalat / the / It / waterfalls / in / beautiful / is / most

=> ………It is the most beautiful waterfall in Dalat………………………………………………………………….

2. over / the / city / Dalat / It’s / two / west / to / of / kilometres

=> ……It's over two kilometers to the west of Da Lat city……………………………………………………………………….

3. the / to / How / are / high / from / bottom / the / falls / top / the/of

=>……………How high are the falls from the bottom to the top……………………………………………………………….

4. tell / the / to / bus / Can / way / you / me / stop / the /?

=> ……Can you tell me the way to the bus stop?…………………………………………………………………….

5. modern / yours / My / more / than / is / house

=> ………My house is more modern than yours…………………………………………………………….

IX. Choose the correct answer for each of the gaps to complete the text.

       Tra Co Beach in Quang Ninh province is 9 kilometers from Mong Cai. It has the (1) _______ and the most romantic beach in Viet Nam. Tourists can enjoy the (2) _______ of white sand beaches and green sea water all year (3) _______. Visitors can (4) _______ enjoy the sunset or sunrise in Con Mang islet. You can visit Tra Co Communal House, Linh Khanh Pagoda, and Tra Co Church.

 If tourists want some fresh (5) _______, they can find it from fishing boats. They can take part in "Tra Co Festival" from May 30 to June 6.

1. A. long                      B. longer                         C. longest        D. much longer

2. A. beauty                   B. beautiful                     C. of beauty    D. pretty

3. A. over                      B. long                            C. round         D. longer

4. A. be                         B. be able                        C. then            D. also

5. A. seafood                 B. menu                          C. air               D. water

X. Rewrite the sentences without changing their meaning.

1. Let’s go to the movie theater. => ………What about going to the movie theater……………………………………

2. My mother needs twelve eggs. => My mother needs a… …dozen eggs………………..

3. Can I help you?  => What………can I do for you?…………………………………………

4. Coffee is her favorite drink => She……likes coffee the most……………………………………

5. It’s very important for you to be here at 6.00.

=> You …………have to be hare at 6.00……………………………………………………

6. Phuc wants to visit Ayres Rock. => Phuc would ……like to visit Ayres Rock……………………

7.  I’ve never seen such a wonderful waterfall before.

     This is the ………most wonderful waterfall I have ever seen……………………………………………………..

8.  How high is Mount Everest?

     What is …………the height of Mount Everest?……………………………………………………..

9.  Shall we go to Ha Long Bay this weekend?

     How about……going to Ha Long Bay this weekend?………………………………………………………..

10. Remember to bring the compass: if not we will get lost in the forest.

=> You must ………bring the compass or we will get lost in the forest……………………………………………………..…

VI. Find and correct mistake.

11. Travelling by tram is most => more convenient than travelling by car in this city   

                             A                 B                           C                        D

12. You must taking =>take off your shoes before entering this room.           

                           A                B                  C                          D

13. You mush brush your tooth =>teeth twice a day.          

                 A           B                 C                  D

14.  He have=> has a dictionary, so he can look up new words easily.             

15. There isn’t some => any water in the bottle                

VII. Choose the correct words to complete the sentences.

1. We had a nice day on the ______________ (coat/ coast).

2. A fishing ____________ (net/ nest) is used on fishing boats for catching fish.

3. The sun rises in the ________(eat/ east) and sets in the ________ (wet/ west).

4. A young ______________ (cat/cast) is called a kitten.

5. This weekend’s weather will be ______________ (wet/ west) and windy.

6. She is the ______________ (bet/ best) student in her class.

7. We took a wrong turn and got______________ (lot/ lost).

8. I really need a new pair of walking ______________ (boots/ boosts).

9. How are you going to France? - We are going by ____________ (boat/ boast).

10. We thanked our ______________ (hot/ host) for a very enjoyable evening.

Ex1:

C

A

A

C

A

B

C

D

A

C

B

C

D

C

A

C

C

A

B

C

A

B

B

D

C

D

A

B

D

B

B

B

C

D

B

A

B

Ex2:

1.natural

2. famous

3. landmark

4.long

5. build

6. beauty

1. She is ill. She mustn’t __________

A. goes out                    B. went out                     C. go out         D. going out

2. This room is too small for my family. I need a __________ one.

A. larger                        B. the largest                   C. large           D. largest

3. I know him __________than you do.

A. better                        B. more well                   C. good           D. the best

4. My salary is __________his salary.

A. high                          B. more high    C. higher than      D. more higher than

5. He works __________we do.

A. harder than               B. as hard as                    C. hardest        D. so hard as

6. No one in this class is __________ Jimmy.

A. so taller than     B. taller than          C. the tallest                    D. more tall than

7. Sarah is __________ at Chemistry than Susan.

A. good                         B. well                            C. better          D. best

8. Sam is a terrible footballer. He is _________player in the team.

A. young                       B. younger than              C. younger      D. the youngest

9. How long are they going to stay there? _____ a week.

A. for                            B. at                                C. in                D. on

10. _____sports do you play?       A. What’s B. How        C. Which     D. Where

11. We _________ get up early to be at the campsite in time.

A. can                           B. must                           C. can't            D. mustn't

12. You _________throw the rubbish into the West Lake.

A. may                          B. must                           C. mustn't        D. may not

13. We ______ hold a party tonight but we ______make some loud noises affecting our neighbours.

A. must/ mustn't            B. mustn't/ must              C. can/ must    D. can/ mustn't

14. You _________take photos in this museum. It’s against the ruler.

A. Must                         B. can                              C. mustn't    D. don't have to

15. You _________ put the rubbish into the bin

A. Must                         B. mustn't                        C. has to           D. don’t have to

16.  I _________ do my homework. My teacher said so.

A. Can                           B. mustn't                        C. have to       D. don't have to

17. You _________ speak on the mobile phone on an aeroplane.

A. Can                           B. must                           C. mustn't          D. don’t have to

18. English is thought to be _________ than Math.

A. harder                       B. the more hard             C. hardest           D. the hardest

19. You _________ travel alone to the mountain. Always go in a group.

A. must                         B. mustn't                        C. do               D. don't

20. They’ve put some lovely ………. in the city park.

A. benchs                      B. benchies                      C. benches                    D. bench

21. You _________ take a lot of warm clothes when you go to Sa Pa in winter

A. must                         B. mustn't                        C. can             D. can't

22. Before they go, the need to buy some _________

A. cloths                       B. clothes                        C. cloth              D. clothe

23. Yeah, I’m going to finish this exercise. I’m sorry I’m such a lazy ass, but I can’t get rid of my _________ you see.

A. laze                   B. laziness             C. lazily                 D. lazyment

24.  “Must I finish my homework now?”  “_________”

A. Yes, you may.   B. Yes, you need.    C. No, you can’t.    D. No, you needn’t

25. “Is there any ____________ in the fridge?” _____ “No, there isn’t any left”

A. vegetable                  B. carrots                        C. milk            D. cake

26. You __________ look at other students’ work. It’s against the rules.

A. must                         B. should                         C. shouldn’t    D. mustn’t

27. How do you go to school? ____ I go to school _________

A. on foot                      B. by foot                        C. with foot    D. in foot

28. You ____________ be late for school. It's against the school regulations.

A. must                         B. mustn't                        C. can             D. can't

29. Peter: “Would you like some more tea?" ~ John: " _______"

A. Yes, give me some      B. Yes, you would           C. No, I won't  D. No, please

30. There ____________ very ____________work to do.

A. isn’t…. many        B. isn’t…much       C. aren’t….many     D. aren’t…much

31. Bad news ____________ make people happy.

A. don’t                         B. doesn’t                          C. isn’t                   D. aren’t

32. The sign says “No smoking “. You __________ smoke.

A. can                           B. must not                     C. are not        D. must

33. __________you writing a letter to Thanh?

A. Is                              B. Do                              C. Are             D. Does

34. Travelling on mountains is really dangerous, so you __________ go alone.

A. should                      B. can                              C. must           D. mustn’t

35. You __________ pick up flowers in the school garden.

A. must                         B. mustn’t                       C. can’t           D. should

36. She must ____ a car carefully.     A. drive      B. drives  C. driving  D. to drive

37. _________ tell me the way to the police station?

A. Would                      B. Can                             C. May            D. Should

V. Put the correct form of the word in the following sentences.

1.Great Wall is one of the …natural…………….  wonders of the world. (nature)

2.My parents are proud of me because I’m a …………famous………singer. (fame)

3. It is an …………amazing………………landmark of the world. (amaze)

4. This river is so ………………long………… (length)

5.They are going to …………build……………… a new bridge near here. (building)

6. I like the ………………beauty…………of the romantic river. (beautiful)

2499 

Khoảng cách : \(2\)

Số lượng số hạng : \(\dfrac{99-3}{2}+1=49\)

\(\Rightarrow3+5+7+...+99=\dfrac{\left(3+99\right).49}{2}=2499\)

2499 nha

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