a)5x^2y-10xy^2

=5xy(x-2y)

b)13x^4y^3-26x^2y^2z^2-39xy^2z^3

=13xy^2(x^3y-2xz^2-3z^3)

c)9x^2y^2+15x^2y-21xy^2

=3xy(3xy+5x-7y)

d)1/2x(x^2-4)+4(x+2)

=1/2x(x-2)(x+2)+4(x+2)

=(1/2x^2-x)(x+2)+4(x+2)

=(x+2)(1/2x^2-x+4)

Gọi a,b,c là số học sinh ba khối 6,7,8

Số học sinh ba khối tỉ lệ với 10;9;8 nên \(\dfrac{a}{10}=\dfrac{b}{9}=\dfrac{c}{8}\)

Số học sinh khối 8 ít hơn khối 6 là 50 học sinh nên \(a-c=50\)

Áp dụng dãy tỉ số bằng nhau ta có

\(\dfrac{a}{10}=\dfrac{b}{9}=\dfrac{c}{8}=\dfrac{\left(a-c\right)}{10-8}=\dfrac{50}{2}=25\)

\(\dfrac{a}{10}=25\) nên a=25.10=250

\(\dfrac{b}{9}=25\) nên b=25.9=225

\(\dfrac{c}{8}=25\) nên c=25.8=200

Vậy số học sinh ba khối là 250;225;200

1. He has taught hundreds of young people.

2. There are 30 schools of rock in the USA.

3. Paul started his first rock school in 1998.

4. The film School of Rock is about a real music school which is run by Paul Green.

5. He teaches his students to played in front of a real audience.

1. recognization 

2. religious

3. suggestion

4. unforgettable

5. enjoyment

6. entrance

7. financial

8. geological

9. contestants 

10. wooden

11. recognition     

12. geographical  

13. pictureque  

14. administrative

15. contestant

16. astounding

17. Religious 

18. defensive

19. sightseeings  

20. location    

1. Their results are different from our results

2. The price of the scarf is the same as the price of the gloves

3. This house is different from your last house

4. The height of the child is the same as the height as the table

5. Jane is different from her sister

6. The taste of this cake is the same as the taste of that cake 

7. Food in San Francisco is different from food in New Orleans

8. His shoes are the same as my shoes

9. American English is differnt from British English 

10. I am the same as my mom

D. foreign country : nước ngoài

Câu B là ngành báo chí câu này đang nói về nghề nghiệp còn đáp án C là nhà báo

In one's view / opinion : theo quan điểm của ai đó

16.C

17.A

18.B

19.D ( radio station ) : đài phát thanh

20.B

21.A

22.C

23.B

24.D

25.A