`A=x^2+6x+y^2+4y+15`

`=(x^2+6x+9)+(y^2+4y+4)+2`

`=(x+3)^2+(y+2)^2+2`

Vì `(x+3)^2+(y+2)^2 >=0 forall x,y`

`=>A_(min)=2 <=> x=-3; y=-2`.

Chủ động -> bị động:

The librarian said a new system was being started because books were not being returned.

*Gián tiếp -> trực tiếp.

"We are starting a new system because people are not returning books." said the librarian.

- Đưa coin thì tham gia, chỉ viết văn, không đọc. :D

- Được nhớ. :D

- Tham gia đi mọi người ơi, được coin đấy. :DDDD

1. He often reads newspapers on his way to the office.
2. One of my favorite subjects is English.
3. Our country has a lot of rivers and mountains.
4. Nam usually has lunch at half past eleven.
5. I am living in a small house with my family in Hoa Lu.
6. Sports and games play an important part in our life.
7. We often play table tennis and do aerobics in summer.
8. I sometimes go swimming with my friends at the weekend.
9. I don't like playing basketball because I am very short.
10. They are playing soccer with their friends in the park now.
.
1. I haven't worn that shirt since May.
2. It's ages since we last met.
3. Travelling by train is not as expensive as traveling by air.
4. What subject do you enjoy most at school ?
5. The last time I visited my family was in 2005.
6. My parents have lived in New Zealand since 2010.
7. I think Paris is the most beautiful city in the world.
8. I don't have enough money to buy the computer.
9. If you don't study harder, you won't pass the exam.
10. Matt hasn't finished his homework yet.

1. peaceful

2. prayers

3. friendliness

4. instruction 

58. B

59. C

60. A

61. A