`-1/2=x-1/6`

`x=-1/2+1/6`

`x=-1/3`

1. B

2. D

1. have been cleaning
2. hasn't bought
3. has gardened
4. have been waiting - hasn't arrived
5. has written
6. have lived
7. has gone
8. has taught
9. have been writing
10. have seen
11. have you know - have known
12. have been building
13. have been studying 
14. has run
15. has played

1. She is given food every day.

2. Buses are caught to work every day.

3. Wine wasn't drunk yesterday.

4. Tables aren't made.

5. A new film is being watched now.

6. A car can be driven.

7. Vietnamese should be studied by Tom.

8. The homework is going to be done.

9. English is learned every day.

`P \in Z <=> (2\sqrtx-1) vdots (\sqrtx+1)`

`<=> [(2\sqrtx+1)-2] vdots (\sqrtx+1)`

`<=> (\sqrtx+1) \in {-2;2;-1;1}`

`<=> \sqrtx \in {-3;1;-2;0}`

`<=> x \in {1;0}`

.

ĐK: `x>=0`.

`P=(2\sqrtx-1)/(\sqrtx+1)=2-2/(\sqrtx+1)`

`x>=0`

`<=> \sqrtx>=0`

`<=> \sqrtx+1>=1`

`<=>2/(\sqrtx+1) <= 2`

`<=> -2/(\sqrtx+1) >= -2`

`<=> 2 - 2/(\sqrtx+1) >= 0`

`<=> P >=0`

Dấu "`=`" xảy ra `<=> x=0`

`P_(min)=0 <=> x=0`.

`(2n+1)/(n+1)` có giá trị nguyên `<=> (2n+1) vdots (n+1)`

`<=> [(2n+2)-1] vdots (n+1)`

`<=> -1 vdots (n+1)`

`<=> n+1 \in Ư(-1)`

`<=> n+1 \in {-1;1}`

`<=> n \in {-2;0}`.

2. D

3. B

4. C

5. A

.

1. think

2. likes

3. took - went

4. painting

5. retires - will go

6. Does....like making

7. promises - will give
8. won't continue
9. plays
10. will dance
.
1. chess
2. dolls
3. music
4. gymnastics
5. go
6. books
7. fishing
8. camping
9. bottles
10. cooking