Ta có góc BCD = 50 + 70 = 120 độ

Lại có góc ABC + BCD = 60 + 120 = 180 độ

Mà 2 góc ở vị trí trong cùng phía

=> AB // DC

\(M=4x\left(x+y\right)\left(x+y+z\right)\left(x+z\right)+y^2z^2=4\left(x^2+xy+xz\right)\left(x^2+xy+xz+yz\right)+y^2z^2\)

Đặt \(x^2+xy+xz=a\) , ta có:

\(M=4a\left(a+yz\right)+y^2z^2=4a^2+4ayz+y^2z^2=\left(2a+yz\right)^2\)

\(M=\left(2x^2+2xy+2xz+yz\right)^2\)là số chính phương với \(x;y;z\in N\)

1. Who did he go on holiday with ?

2. What did she do ?

3.Whose dictionary did you borrow ?

4. Who gave some money to Mike ?

5. Who helped John with his homework yesterday ?

6. Where did she leave her suitcase ?

7. When did she last ride a bike ?

8. How many kilo of cheese did you buy ?

9. What did he do two day ago ?

10. Who did you go to the cinema with ?

11. How many kilo of oranges did you buy ?

12. Who did John write about ?

13. What did she make for her mother ?

5/a - b/3 = 1/6

=> 5/a = 1/6 + b/3

=> 5/a = 1/6 + 2b/6

=> 5/a = ( 2b + 6 )/6

=> ( 2b + 6 ) . a = 5 . 6 = 30

=> 2b + 6 và a \(\in\) Ư ( 30 ) = ( 1, 2, 3, 5, 6, 10, 15, 30 ) vì a,b nguyên tố nên Ư của 30 phải dương

Gọi số gạo thùng thứ 1 và 2 là a và b ( a, b > 0 )

Ta có a + b = 60

Theo đề bài ta có :

a - 25%a + b + 25%a = 60

a - 1/4a + b + 1/4a = 60 ( 1 )

Mà a - 1/4a = b + 1/4a

Thay a - 1/4a vào b ở ( 1 ) có :

a - 1/4a + a - 1/4a = 60

3/4a + 3/4a = 60

3/2a = 60

a = 40

b = 20

A.Oh, yes. What is it? ( 3 )

B.Dad? ( 1 )

C.The Spiderman ( 4 )

D.Yes ( 6 )

E.Are you going to see it? ( 5 )

F. There is a good film on in this town ( 2 )

G.I'd like to - but I don't have money ( 7 )

1. If I (be)...were........ you, I (get)............would get......... that job.
2. If I (have) ........had....... free time now, I (sleep) ..............would sleep..........
3 If she (be)......were......... a man, she (fell)...........feel..... better.
4. If today (be ) .....were ............... my birthday, I ( get )..would get............ a lot of presents.
5. If the global temperature (not rise).....did not rise.........., many severe disasters (not occur)........would occur.........
6. If the environment (be not)........were not............. polluted, people's health (be) ...........would be..... better.
7. If you..........helped.............. (to help) your grandma, I....would do........(to do) the shopping.
8. Andrew.........would water...... (to water) the flowers if he..stayed.........(to stay) at home.
9. If she ......had......... (to have) 5 pounds more, she ........would buy..... (to buy) herself this T- shirt.
10. If they .....offered..............(to offer) me the job, I .....would take...(to take) it.
11. You.........would have.....(to have) summer holidays from June till August if you....lived............ ( to live) in the USA.
12. We.....would sell.............( to sell) the bike for 20 Euros if Ron.....repaired...............(to repair) it.
13. If you .........used............... ( to use) a pencil, the drawing....would be.............(to be) perfect.
14. The children..........would be............(to be) happy if he.......taught........(to teach) them English.
15. If Ireen...........visited.............(to visit) us, we ..........would go.............(to go) out tonight.
16. They ...............would come........(to come) again if he......planed............(to plan) a second stay.

7/polite / impolite

8/ independent / dominate

9/ boring / interesting

10/ helpful / futile

1/ talkative / taciturn

2/ shy / brave

3/ hard-working / lazy

4/ studious / lazy

5/ kind / sinister

6/ optimistic / pessimistic

7/polite

8/ independent

9/ boring

10/ helpful