Giả sử 2≤b≤a<c có a(a+1)=c(c+1)−b(b+1)=(c−b)(c+b+1)      (1)

Do a+1<c+b+1 từ (1)⇒c−b<a⇒c<a+b⇒c+b+1<a+2b+1⇒c+b+1<3a+1

c>a⇒c+b+1=2a hoặc c+b+1=3a

Vì a,b,c là các số nguyên tố , c>a⇒c lẻ ta có 2 trường hợp

TH1: c+b+1=2a; Do c+1 và 2a là số chẵn thì b là số nguyên tố chẵn nên b chẵn nên b=2

  Từ đó tìm ra 3a=11 (loại)

TH2: c+b+1=3a thay vào (1) có a+1=3(c−b) mà c=3a−b−1⇒a+1=3(3a−2b−1)⇒3b=4a−2⇒b chẵn ⇒b=2⇒a=2⇒c=3

Em chỉ cần vào tài khoản google của mk là lấy lại được à^^

lần trước cũng đột nhiên không vào được nên người ta hướng dẫn thế đó,cứ làm theo các bước người ta hướng dẫn là lấy lại đc cái cũ à^^

1 ) Mary asked me " Do you want to visit London ?"

=> Mary asked me if I wanted to visit London.

2 ) They have just built a new school near my housr .

=> A new school near my house has just been built .

3 ) I study English because I want to talk to foreigners

=> I study Eg so I can talk to foreigners.

4 ) To do morning exercises every day is good for our health .

=> It's good for our health to do morning exercises every day.

I,

1.I'm learning very hard these days.........get good marks at my exem

A.that B.in order C.in order to D.in order that

2.Cloth bags..........used instead of plastic bags

A.are B.is C.are used D.are useing

3.Would you mind if she...........you?

A.phoned B.phoned to C.phoning D.is phoned

4.This is a machine which is used to wash clothes.It's a..........

A.clothes-washing machine B.washing machine-clothes

C.clothes-machine washing D.machine washing-clothes

5.This project...........at the end of this month

A.will B.finshing C.will be finished D.finished

6.Household and garden waste.................collected.........compost

A.is/to make B.are/to do C.is/to do D.are/to make

7.She asked if many tourist ...............to visit My Son in summer.

A.want B.will want C.wanted D.were wanting

8.It was late,so we decided...........a taxi home

A.take B to take C.talking D.took

9.Tim said he..........a chocolate factory then

A.visited B.are visting C.has visited D.was visiting

10.She ...........a movie tonight

A.see B.seeing C.is going to see D.saw

II,

1.She asked if many tourist ...............to visit My Son in summer

A.want B.will want C.wanted D.werw wanting

2.They showed me where.......tickets

A.get B.got C.to get D.getting

3.Thanks for.......met to the rice cooking festival

A.to invite B.invite C.invites D.inviting

4.I asked her.........she was enjoying her dinner

A.whether B.in case C.invites D.unless

5.That test is.......tomorrow

A.going done B.go done C.going to be done D.going to be doing

6.A bill......to you at the end of the month

A.will send B.will be sent C.will send D.will be seing

7..................is a very deep narrow valley,usualy with a river flowing throught it

A.Canyon B.Reef C.Cave D.Bay

8.I don't know what..........

A.to do B.for doing C.to be done D.be done

9...........is a person whose job is to put in and repair pipes and baths

A.Plumber B.Gardener C.Florist D.Inventor

10.The..........festival is a festival in which people have their bulls fight against each other

A.whale watching B.bull-fighing C.moutain-climbing D.ice-sakting

III,

1.He had his father........his watch

A.fixed B.fixing C.to fix D.fix

2.Jane really enjoys ........to dinner parties

A.inviting B.being inviting C.being invited D.be invited

3.Economics.......as interesting to me as literature

A.doesn't B.haven't C.isn't D.aren't

4.This soup is very hot,but I always think the.........the better

A.hotter the B.hottest C.hotter D.hot the

5.After a month,Hoa got used to.....in her new school

A.Study B.studying C.studied D.is studying

6.He worked hard.........he could pass the final exam

A.so that B.in order to C.so as so D.ass result

7.They........me if I could speak Japanese

A.told B.said C.asked D.talked

8.Are you proud.................your country and its tradition?

A.about B.on C.of D.for

9........the news bad?

A.are B.is C.were D.are there

10.The were......flowers that I couldn't decide what to buy

A.so many B.so few C.so little D.so much

11.My sister likes sweets......from chocolate

A.making B.made C.to make D.make

12.What is he laughing..........?

A.over B.by C.into D.at

13.We arrived ...............the station half an hour late

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

14.My brother and I............

A.am having a wonderful time here B.am having a wonder time here

C.are having a wonderful time here D.are having a wonder time here

15.The guide...........some interesting things

A.told B.spoke C.said D.talked

16"Pass me that pen please".-"............."

A.no,it isn't B.here you are C.yes,please D,it doesn't matter

17.I'm bored ......sleeping and watching all day.

A.up B.of C.with D.about

18.Why don't you........with your university study?

A.go in B.go on C.go by D.go at

19.Of my parents,my father is.......

A.more stricter B.the strictest C.strict D.stricter

20.Who is going to........the phone?

A.reply B.respond C.answer D.pick

Find the word with the different underline sound.

1. A.washed B.needed C.danced D.matched
2. A.obey B. key C. grey D. survey

3. A.ways B. days C. says D. stays

Find the word with has a different stress pattern from the others.

4. A. prefer B. finish C. complete D. begin

5. A. dangerous B. important C. enormous D. convenient.

1)Mg + H₂SO₄ ----> MgSO₄ + H₂

2)MgO + H₂SO₄ ---->MgSO₄ + H₂O

3)Mg(OH)₂ + H₂SO₄ ---> MgSO₄ + H₂O