Ta có: `1>=a+b>=2\sqrt(ab)=>ab <=1/4`

Áp dụng BĐT Côsi và `1/x+1/y>=4/(x+y)(x;y>0)` ta có:

`E=1/(a^2+b^2)+1/(ab)+4ab=(1/(a^2+b^2)+1/(2ab))+(1/(2ab)+8ab)-4ab>=4/(a^2+2ab+b^2)+2\sqrt(1/(2ab) . 8ab)-4ab=4/(a+b)^2+4-4ab>=4+4-1=7`

Dấu '=" xảy ra `<=>a=b=1/2`

Vậy `E_(min)=7<=>a=b=1/2`

1. C. would rather
2. A. character
3. C. satisfied
4. A. to have
5. C. passed away
6. A. alone / lonely
7. D. minute is
8. D. identical
9. C. destroy
10. C. better not
11. A. items
12. B. should work
13. A. arrive
14. A. above
15. B. so that
16. D. keep
17. C. into
18. A. to accept
19. A. daughter
20. C. loss
21. B. No worries. Come in, please.
22. D. it’s right up your street!

16. Our father has taken us to the collective farm a few times.

17. Someone is cutting down the trees along the street.

Theo mình nghĩ đề sẽ là chuyển tù câu bị động `->` câu chủ động(vì mấy câu trước bạn đăng thấy mọi người trả lời thế).

16. Our father has taken us to the collective farm a few times.

17. Someone is cutting down the trees along the street.

Yêu cầu đề là gì thế bạn?

1. I suggested that Ba turn off the lights when leaving the classroom.
2. Ms. Xuan gets a good salary because she types very fast.
3. My son is continuing to study English in that language centre because he wants to improve his English skills.
4. If we buy recycled products, we can do our part to save natural resources.
5. If you don't save electricity and water monthly, you'll have to pay a lot of money.
6. I suggested that you wash your hands often with soap and water to prevent infection.
7. How about we put the garbage bins around the schoolyard?
8. If you don't do the work carefully, I will punish you.
9. As he couldn't cook a meal, he went to the restaurant.
10. Miss Lan is trying to look for a good way to reduce her electricity bill.

Với `p;q;r;s\inRR : {(p+q+r+s=0),(p<q<r<s):}` chứng minh rằng: `p<1/2 \root[3]{(\sqrt(24(pq+pr+ps+qr+qs+rs)^3+81(pqr+qrs+rsp+spq)^2)+9(pqr+qrs+rsp+spq))/(9)}-(pq+pr+ps+qr+qs+rs)/(\root[3]{3\sqrt(24(pq+pr+ps+qr+qs+rs)^3+81(pqr+qrs+rsp+spq)^2)+27(pqr+qrs+rsp+spq)})<s`

Ta thực hiện phép chia `787` cho `5` ta có: `787` chia `5` đượcc thương là `157` và dư `2`

`->` Cần ít nhất `157+1=158` ghế để chứa hết học sinh trường THCS này.

Đáp số: `158` ghế

1. choose
2. go
3. take
4. mark
5. meet
6. have
7. don't

1. Ba always walks to school.
2. The Mekong River is longer than the Red River.
3. Ho Chi Minh City is the biggest city in Vietnam.
4. How much rice does he produce?
5. She will visit Ha Long Bay this summer vacation.
6. What is the most expensive car?
7. My brother has been going to Ho Chi Minh City since 2012.
8. If you work hard, you will pass the exam.
9. In the years 2030, robots will be able to do all the housework for us.
10. Although I was ill yesterday, I went to school.