giúm mình làm bài này với ạ
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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.
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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