1. When / it / nice / family / spend / weekend / grandparents / farm.

--> When it is nice, my family spends the weekend on our grandparents' farm.

2. Trash / pollute / land / rivers / oceans .

--> Trash pollute land, rivers and oceans.

3. When / not / need / light / turn / off .

--> When you don't need light, turn it off.

4. Smoke / factories / a cause / air pollution .

--> Smoke from factories is a cause of air pollution.

5. What / you / want me / buy / you ?

--> What do you want me to buy for you?

6. I / not hungry / but / thirsty / and / like / glass / water .

--> I am not hungry but I am thirsty and I would like a glass of water.

7. It / hot / Viet Nam / April ?

--> Is it hot in Viet Nam in April?

a_ cm tam giac ABD= tam giac BED ( ch-gn)--> BE=BA va AD=DE-> Bva D nam tren duong trung truc cua AE-> BD la duong trung truc AE

b_ cm tam giac DFA= tam giac DCE (g-c-g) DA=DE, Goc DAF= goc DEC (=90), ADF=EDC ( doi dinh)-> DF=DC

c_tu diem D den duong thang EC ta co 

DE la duong vuong goc, DC la duong xien --> DE<DC ( quan he duong xien duong vuong goc)

ma DE=DA ( tam giac ABD= tam giacBED)

nen DA<DC

d) tu diem B den duong thang EF ta co :

BE la duong vuong goc , BF la duong xien--> BE<BF ( quan he duong xien duong vuong goc)

tu diem C den duong thang EF ta co

CE la duong vuong goc, CF la duong xien -> EC< CF  (quan he duong xien duong vuong goc)

--> BE+EC < BF+CF

---> BC < BF+CF

ma BD+DC < BC ( bdt trong tam giac BDC )

nen BD+DC < BF+CF

\(a,\frac{3}{5}\times\frac{7}{9}=\frac{3\times7}{5\times9}=\frac{3\times7}{5\times3\times3}=\frac{7}{5\times3}=\frac{7}{15}\)

\(b,\frac{9}{13}\times\frac{17}{18}=\frac{9\times17}{13\times18}=\frac{9\times17}{13\times2\times9}=\frac{17}{13\times2}=\frac{17}{26}\)

Câu c,d tương tự

EX1: Chọn từ khác loại

1. A.white B.big C.small D.large

2. A.tall B.high C.short D.fast

3. A.bone B.fish C.carrot D.ham

4. A.sea B.lake C.river D.ground

5. A.cat B.rabbit C.dog D.sheep

The animal is ..................

EX2: Chọn từ đúng

1.I often ____ up at 6.00 every morning but I stay in bed till 6.15.

A.wake B.get C.go D.stay

2.My aunt is a vegetarian. She never _______ meat or fish at the shop.

A. drinks B.has C.buys D.eat

3.My younger brother likes ______ cartoon films after school.

A.seeing B.watching C.looking D.listening

4.Her farther is a/an ________. He love colors and creativity.

A.farmer B.doctor C.engineer D.artist

5.Ann: It's three thirty, now.

Bob: _____________, thank you.

A. Half past three B.Three past thirty

C.Three half D.Over three

EX3: Sắp xếp

1. last Sunday/ father/ bike/ repaired/ my/ my

--> My father repaired my bike last Sunday.

2.people/ there/ are/ family/ how many/ your/ in?

--> How many people are there in your family?

3.have/ we/ Math/ Science/ and/ Tuesday/ on

--> We have Math and Science on Tuesday.

4.she/ from/ Australia/ , /is/ she/ isn't?

--> She is from Australia, isn't she?

5.write/ table/ on/ don't/ the/ please.

--> Please don't write on the table.

EX4: Hoàn thành các câu( Tùy thích)

1. My brother is a doctor. (Nghề nghiệp)

2.Her younger sister iss helpful. ( Như thế nào)

3.Our city is noisy (Như thế nào)

4.In my free time, I listen to music. (Làm gì)

5.Vietnam is beautiful.( Như thế nào)

1. About fifty million people are watching this program.

--> This program are being watched by about fifty million people.

2. You mustn't touch this button while the experiment is in progress.

--> The button musn't be touched while the experiment is in progress.

3. They took the old man to hospital.

--> The old man was taken to the hospital.

4. When did they open that hospital?

--> When was that hospital opened?

5. Someone has opened this letter.

--> This letter has been opened.

6. People consume gas faster than they produce it.

--> Gas is consumed faster than they produce it.

7. They should reduce air pollution.

--> Air pollution should be reduced.

8. No one has seen him any where this week.

--> He hasn't been seen anywhere this week.

9. They have made every effort to recover the stolen painting.

--> Every effort has been made to recover the stolen painting.

10. They are repairing this road at the moment.

--> This road is being repaired at the moment.

11. Bad weather has delayed the plane for one hour.

--> The plane has been delayed for one hour by bad weather.

12. Are they building the highest tower in the city centre?

--> Is the highest tower in the city centre being built?

\(1\text{) }a^3+b^3+c^3=3abc\Leftrightarrow\frac{1}{2}\left(a+b+c\right)\left[\left(a-b\right)^2+\left(b-c\right)^2+\left(c-a\right)^2\right]=0\)

\(\Leftrightarrow a+b+c=0\text{ hoặc }a-b=b-c=c-a=0\)

\(\Leftrightarrow a+b+c=0\text{ hoặc }a=b=c\)

\(\text{+TH1: }a+b+c=0\Rightarrow a+b=-c;\text{ }b+c=-a;\text{ }c+a=-b\)

\(B=\frac{b+a}{a}.\frac{c+b}{c}.\frac{a+c}{b}=\frac{\left(-c\right)\left(-a\right)\left(-b\right)}{abc}=-1\)

\(+\text{TH2: }a=b=c\)

\(B=\left(1+1\right)\left(1+1\right)\left(1+1\right)=8\)

\(2\text{) Ta có: }a^3+b^3+c^3=\left(a+b+c\right)\left(a^2+b^2+c^2-ab-bc-ca\right)+3abc\)

\(\Rightarrow0=0+3abc\Rightarrow abc=0\)

\(\Rightarrow a=0\text{ hoặc }b=0\text{ hoặc }c=0\)

Không mất tính tổng quát, giả sử c = 0.

\(a+b+c=0\Rightarrow a+b=0\Rightarrow a=-b\)

\(C=\left(-b\right)^{2013}+b^{2013}+0^{2013}=0\)

1. They / not/see/each other /months .

=>They haven't seen each other for months.

2. The sun/shine /brightly /when she / came .

=>The sun was shining brightly when she came.

3. I/invited / her birthday party /last week .

=>I was invited to her birthday party last week.

4. She/used/stay/her uncle/when/a child .

=>She used to stay with her uncle when she was a child.

5. It/be/ important /students/do exercises / before/go/class .

=>____________________________- .