38.

$\sqrt{2006}-\sqrt{2005}=\frac{2006-2005}{\sqrt{2006}+\sqrt{2005}}=\frac{1}{\sqrt{2006}+\sqrt{2005}}< \frac{1}{\sqrt{2005}+\sqrt{2004}}=\frac{2005-2004}{\sqrt{2005}+\sqrt{2004}}=\sqrt{2005}-\sqrt{2004}$

39.

$\sqrt{1998}+\sqrt{2000}-2\sqrt{1999}=(\sqrt{2000}-\sqrt{1999})-(\sqrt{1999}-\sqrt{1998})$

$=\frac{1}{\sqrt{2000}+\sqrt{1999}}-\frac{1}{\sqrt{1999}+\sqrt{1998}}$

$< 0$

$\Rightarrow \sqrt{1998}+\sqrt{2000}<2\sqrt{1999}$

Bài 40 bạn làm tương tự câu 38.

Câu 1 : Ở ngô 2n = 20 

Kì sau giảm phân II

- Số NST đơn : 2n =20

- Số cromatit : 0

- Số tâm động : 20

Câu 2: Đậu Hà lan : 2n = 14

Kì cuối GPI

- Số NST kép : n = 7 

- Số cromatit: 14

- Số tâm động: 7

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(Your name)

... bn check lại đề chỗ chất D nhé, tính bị sai á

mình nghĩ "thu được 12,8 gam khí SO₂" hợp lý hơn :)

THAM KHẢO:

24. A. are coming B. will have come C. were going to come

25. A. will perform B. are performing C. we going to perform

26. A. will give B. are going to give C. were going to give

27. A. sell B. are selling C. will have sold

28. A. go B. will go C. are going

29. A. will book B. am going to book C. will have booked

30. A. leave B. are leaving C. are going to leave

31. A. won’t be B. won’t have been C. am not being

32. A. am going to rehearse B. will rehearse C. will be rehearsing

33. A. will start B. was going to start C. will have started

Ta có: ΔABC∼ΔDEF

nên DE/AB=EF/BC=DF/AC

=>9/6=EF/10=DF/14

=>EF/10=DF/14=3/2

=>EF=15cm; DF=21cm