ta có a+c>b suy ra (a+b+c)^2>4b^2 suy ra (a+b+c)^2+(a-b+c)^2>(a+b+c)^2>4b^2

bóng vàng + bóng đỏ = 11 quả

nếu bóng vàng lớn hơn hoặc bằng 6 thì bóng vàng lớn hơn bóng đỏ

và bóng vàng nhiều hơn bóng xanh nên bóng vàng có 5 quả

suy ra bóng đỏ 6 quả

1.were

2.would feel

3.were

4.would finish

5.would come

6.had opened

7.had left

8.had come

9.would come

10.had given

1.will give

2.would type

3.paid

4.can save

5.knew

6.will have

7.would not

8.were

9.finds

10.will be

1. If you get the first prize, we _____ a celebration.

      A. have                       B. will have                 C. would have had      D. would have

2. If she _____ such mistakes again, she'll lose her job.

      A. made                      B. makes                      C. had made                 D. make

3. If he had much money, he _____ one villa.

      A.  is buy                    B. could buy               C. can buy                     D.  will buy   

4. If it _____, I will come to see you.

      A. didn't rain             B. doesn't rain            C. don't rain                  D. not rain

 5. I _____ to work if I had a car.

      A. drove                     B. will drive                C.  would drive            D. would have driven

6. If there were no gravity, everything _____.

      A. would float           B. floated                    C. would be floating   D. will float

7. Unless you go now, you _____late for school.

      A. will be                   B. would have been   C. would be                  D. are

8. You______ if you take a map.

      A. will get lost           B. would get lost        C. won't get lost           D. would have got lost

 9. We would save thousands of lives if we ______out the remedy for the flu.

      A. had not found      B. found                      C. find                           D. will find

 10. If I _____ ten years younger, I would do yoga every day.

      A. are                          B. were                        C. have been                D. am

11. If we _____ in a town, life would be better.

      A. had lived               B. lived                        C. would live                D. live

 12. We _____ you if we have time.

      A. would phone        B. had phoned            C. phoned                     D. will phone

13. It _____ be a pity if she married Fred.

      A. can                         B. would                      C. may                           D. will

14. I know I'll feel better if I _____ smoking.

      A. stopped                 B. will stop                  C. stop                           D. had stopped

15. I could understand him if he _____ more slowly.

      A. speaks                   B. spoke                      C. would speak            D. had spoken

16. The kitchen will look better if it _____ red curtains.

      A. have                       B. had had                   C. would have              D. has

17. It _____ quicker if you use a computer.

      A. would be               B. will be                     C. been                          D. were

 18. "Will you come to the party tomorrow?" - "I will if I_____ no visitors."

      A. had                         B. will have                 C. have                          D. am having

19. If they didn't live so far away, I _____ them every week.

      A. will visit                B. visited                     C. visit                           D. would visit

 20. Unless we _____ throwing garbage into the ocean, it will be polluted.

      A. won't stop             B. stop                         C. will stop                   D. don't stop

câu đk loại 1 : S + Vs,es + O , S + will/can + Vbare +O

câu đk loại 2 : S + Ved/c2 + O , S + would/could + Vbare + O

Dặm là một đơn vị chiều dài, thường được dùng để đo khoảng cách, trong một số hệ thống đo lường khác nhau, trong đó có Hệ đo lường Anh

3.D       4.A       5.B      6.A      7.C      8.B      9.C      10.D

11.B     12.D     13.A     14.D      15.A       16.C

V.   

1.D    2.B     3.C     4.D    5.B

a. \(N=\left(\dfrac{x+2}{x\sqrt{x}+1}-\dfrac{1}{\sqrt{x}+1}\right).\dfrac{4\sqrt{x}}{3}\)  \(\left(ĐKXĐ:x\ge0\right)\)

\(N=\left(\dfrac{x+2}{x\sqrt{x}+1}-\dfrac{x-\sqrt{x}+1}{x\sqrt{x}+1}\right).\dfrac{4\sqrt{x}}{3}\)

\(\text{​​}\text{​​}N=\dfrac{\sqrt{x}+1}{x\sqrt{x}+1}.\dfrac{4\sqrt{x}}{3}\)

\(N=\dfrac{4\sqrt{x}}{3\left(x-\sqrt{x}+1\right)}\)

b.\(N=\dfrac{8}{9}\Leftrightarrow\dfrac{4\sqrt{x}}{3\left(x-\sqrt{x}+1\right)}=\dfrac{8}{9}\)

\(\Leftrightarrow3\sqrt{x}=2x-2\sqrt{x}+2\)

\(\Leftrightarrow\left(2\sqrt{x}-1\right)\left(\sqrt{x}-2\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{1}{4}\\x=4\end{matrix}\right.\)

c.\(\dfrac{1}{N}>\dfrac{3\sqrt{x}}{4}\Leftrightarrow\dfrac{3\left(x-\sqrt{x}+1\right)}{4\sqrt{x}}>\dfrac{3\sqrt{x}}{4}\)

\(\Leftrightarrow x-\sqrt{x}+1>x\)

\(\Leftrightarrow x< 1\)

Hóa C55 bài 2a :

Để phục hồi những bức tranh đó người ta phun lên bức tranh nước oxi già H2O2, bức tranh sẽ trắng trở lại

giải thích: Pb(OH)2.PbCO3 lâu ngày tác dụng dần với khí H2S có trong không khí tạo ra PbS màu đen :

Pb(OH)2 + H2S →PbS↓+ 2H2O

Phun dung dịch H2O2 sẽ làm cho PbS chuyển thành PbSO4 màu trắng : PbS + 4H2O2 → PbSO4↓ + 4H2O.