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 Bài này có thể giải bằng cách dùng định lý Menelaus khá ngắn như sau:

 Áp dụng định lý Menelaus cho tam giác ABC với cát tuyến DMK, ta có: \(\dfrac{MB}{MC}.\dfrac{KC}{KA}.\dfrac{DA}{AB}=1\) \(\Rightarrow1.\dfrac{KC}{KA}.2=1\) \(\Leftrightarrow\dfrac{KC}{KA}=\dfrac{1}{2}\) \(\Leftrightarrow KA=2KC\) (đpcm)

 Nhưng nếu bạn chưa được dùng định lý Menelaus thì sẽ phải làm như sau:

 Kẻ BP//AC \(\left(P\in DK\right)\). Khi đó theo định lý Thales, \(\dfrac{MB}{MC}=\dfrac{BP}{CK}\) và \(\dfrac{DA}{DB}=\dfrac{AK}{BP}\). Do đó:

 \(\dfrac{MB}{MC}.\dfrac{KC}{KA}.\dfrac{DA}{DB}=\dfrac{BP}{CK}.\dfrac{CK}{AK}.\dfrac{AK}{BP}=1\), và tới đây ta lại quay về tính như đã trình bày ở trên.

C

b

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Hoàng sa và Trường sa là của VN!!!

37.Chu Dong Chu couldn’t buy any special food. He was very poor.                                          (because)

à_________Chu Dong Chu couldn’t buy any special food because he was very poor.     _________________________________________________________________.

39.No one in my class is as tall as Mono.                                                                                       (the)

à_________Mono is the tallest student in my class_________________________________________________________________.

41.No one in my group is as beautiful as Jane.                                                                             (the)

à___Jane is the most beautiful person in my group_______________________________________________________________________.

43.He spent an hour walking to school last night.                                                                           (took)

It took him an hour to walk to school last night

44.It rained hard,but we still went swimming.                                                                               (Although)

Although it rained hard, we still went swimming

8.Mr.Buong is                          old customer and                    honest man.

9.Giving lucky money to the children or the older is one of the customs we _____on the first day of Tet.

10. He_______ his grandparents on T.V last night.

11.                   youngest boy has just started going to           school.

12.David ________ television at the moment.

13. Please turn off                   lights when you leave                        room.

14. Tet is a Vietnamese festival which  ________ in late January and February.

15. My family often have a tradition of holding a family ______at Christmas.

16. Can you show me              way to             station?

17. ………….his old age, Mr. Brown goes jogging every day.                              

18.Many shops have a lion dance performance at their opening ______.

19. I’m going to tell you something important,so please listen more______.

20. They suggested…………..the T.V to watch the weather forecast.

21. She has read                       interesting book.

22. “We‘re going on a trip to Ha Long Bay next week.” “Really? _______!”

\(D=\dfrac{2x+4}{3x-1}\\ =>3D=\dfrac{6x+12}{3x-1}=\dfrac{2\left(3x-1\right)+14}{3x-1}=2+\dfrac{14}{3x-1}\)

Để 3D nguyên thì : \(\dfrac{14}{3x-1}\in Z\)

\(=>14⋮\left(3x-1\right)\\ =>3x-1\inƯ\left(14\right)=\left\{\pm1;\pm2;\pm7;\pm14\right\}\)

\(=>3x\in\left\{2;0;3;-1;8;-6;15;-13\right\}\\ =>x\in\left\{\dfrac{2}{3};0;1;-\dfrac{1}{3};\dfrac{8}{3};-2;5;-\dfrac{13}{3}\right\}\)

Mà x nguyên \(=>x\in\left\{0;1;-2;5\right\}\)

Do những giá trị trên chỉ là 3D nguyên nên chưa chắc D đã nguyên

Vậy thử lại thay từng giá trị x vào bt D

Kết luận : \(x\in\left\{0;1;-2;5\right\}\)

1 D

2 B

3 A

4 D

5 A

\(a.n_{Fe}=\dfrac{11,2}{56}=0,2mol\\ Zn+FeSO_4\rightarrow ZnSO_4+Fe\\ n_{Zn}=n_{FeSO_4}=n_{Fe}=0,2mol\\ m_{Zn}=0,2.65=13g\\ b.m_{FeSO_4}=0,2.152=30,4g\\ C_{\%FeSO_4}=\dfrac{30,4}{300}\cdot100=10,13\%\)