a) ĐK: x thuộc R

pt <=> \(2x+5=1-x\)

\(\Leftrightarrow3x=-4\Leftrightarrow x=-\dfrac{4}{3}\)

KL:....

b) ĐK: x thuộc R

pt <=> \(x^2-x=3-x\)

\(\Leftrightarrow x^2=3\Leftrightarrow\left[{}\begin{matrix}x=\sqrt{3}\\x=-\sqrt{3}\end{matrix}\right.\)

KL:....

c) ĐK: x thuộc R

pt <=> \(2x^2-3=4x-3\)

\(\Leftrightarrow2x^2-4x=0\Leftrightarrow2x\left(x-2\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=0\\x=2\end{matrix}\right.\)

KL:.....

\(a-b=\sqrt{2}+1;b-c=\sqrt{2}-1\Rightarrow a-c=\sqrt{2}+1+\sqrt{2}-1=2\sqrt{2}\)

Ta có: \(A=a^2+b^2+c^2-ab-bc-ca=\dfrac{2a^2+2b^2+2c^2-2ab-2bc-2ca}{2}\)

\(=\dfrac{(a^2-2ab+b^2)+\left(b^2-2bc+c^2\right)+\left(c^2-2ca+a^2\right)}{2}\)

\(=\dfrac{\left(a-b\right)^2+\left(b-c\right)^2+\left(a-c\right)^2}{2}\)

\(=\dfrac{\left(\sqrt{2}+1\right)^2+\left(\sqrt{2}-1\right)^2+\left(2\sqrt{2}\right)^2}{2}\)

\(=\dfrac{3+2\sqrt{2}+3-2\sqrt{2}+8}{2}=\dfrac{14}{2}=7\)

Vậy, A=7

https://hoc247.net/hoi-dap/toan-9/giai-phuong-trinh-13can-x-2-x-4-9can-x-2-x-4-16-faq424430.html

cái này mik tham khảo đc trên mạng, gửi để bn xem

1. lacquerware

2. conical hats

3. baskets

4. pottery

5. silk

6. paintings

Quy luật: Hiệu giữa số thứ nhất và số thứ hai ở mỗi hàng ngang bằng số còn lại ở mỗi hàng ngang

21-17=4

16-20=-4

18-11=7

15-18=-3

=> chọn f

Em quê ở Nghệ An: 

5 người nổi tiếng cùng quê với am là:

1. Hồ Chí Minh

2. Phan Đăng Lưu

3. Mai Thúc Loan

4. Nguyễn Duy Trinh 

5. Đặng Thai Mai

1. A

2. B

3. D

4. A

5. C 

IV. Choose the best answer.

21. Many of the……..not expect to win.

          A. participants in the race do                          C. participants in the race does

          B. participants in the races does                     D. participant in the race does

22. The English…….strong traditions.

          A. has                     B. have much                   C. have many            D. has much

23. ……moved to that city recently.

          A. A number of Vietnamese have                            C. The number of Vietnamese have

          B. A number of Vietnamese has                              D. The number of Vietnamese has

24. Each of the reference……available in the school library.

    A. books on that list is    B. books on that list are     C. book on that list is          D. book on that list are

25. There ……in the world today.

          A. is many new computer company                         C. are many new computers companies

B. is many new computers company                          D. are many new computer companies

26. The doctor who has visited dozens of countries and has helped thousands of patients all around the world………over there.
                A. is                            B. are                     C. was                               D. were

27. A series of lectures………being presented at the Central Hall this week.

A. are           B. will be            C. has become           D. is

28. Each student………. answered the first three questions.

A. has           B. have              C. have to             D. must

29. Either John or his wife ………breakfast each morning.

A. make          B. is making           C. makes             D. made

30. Everybody who ………. a fever must go home at once.

A. has           B. have               C. is having           D. are having

31. Five dollars ………all I have onme.

A. are            B. is                C. will be             D. have

32. John, along with twenty friends, ………. planning a party.

A. are            B. is                 C. has been           D. have been

33. Mathematics………. . the science of quantity.

A. was           B. are                C. is                 D. were

34. Measles………cured without much difficulty nowadays.

A. is             B. are               C. will be             D. have

35. Neither Mary nor her brothers……a consent form for tomorrow’s field trip.

A. need           B. needs             C. is needing         D. has need

36. Peter, together with his uncle,……………fishing.

A. have gone          B. has gone           C. go               D. goes

37. The army…………. eliminated this section of the training test.

A. has                     B. is having           C. are              D. have

38. The number of the months in a year…………twelve.

A. was                    B. were             C. are               D. is

39. The picture of the soldiers………. . back many memories.

A. will bring         B. brings            C. bring              D. have brought

40. These pictures, as well as the photograph………. . the room.

A. brightens           B. brightening                   C. brighten                            D. being brightened

41. What he told you………. . to be of no importance.

A. seems             B. seem                     C. must seem                       D. have seemed

42. Mr. John, accompanied by several members of the committee,………. . proposed some changes of the rules.

A. have               B. has              C. are                     D. is

43. The flock of birds…………. . circling overhead.

A. gets                B. are            C. is               D. get

44. The levels of intoxication…………. from subject to subject.

A. has been varied           B. have been varied         C. varies           D. vary

30. Advertisements on television…………. . becoming more competitive than ever before.

A. has                     B. have                    C. are                                  D. is

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