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Bạn xem lời giải của mình nhé:
Giải:
\(S=\frac{1}{5}+\left(\frac{1}{13}+\frac{1}{14}+\frac{1}{15}\right)+\left(\frac{1}{61}+\frac{1}{62}+\frac{1}{63}\right)\\ \frac{1}{13}< \frac{1}{12}\\ \frac{1}{14}< \frac{1}{12}\\ \frac{1}{15}< \frac{1}{12}\\ \frac{1}{61}< \frac{1}{60}\\ \frac{1}{62}< \frac{1}{60}\\ \frac{1}{63}< \frac{1}{60}\)
\(\Rightarrow\frac{1}{5}+\left(\frac{1}{13}+\frac{1}{14}+\frac{1}{15}\right)+\left(\frac{1}{61}+\frac{1}{62}+\frac{1}{63}\right)< \frac{1}{5}+\left(\frac{1}{12}+\frac{1}{12}+\frac{1}{12}\right)+\left(\frac{1}{60}+\frac{1}{60}+\frac{1}{60}\right)\)
\(\Rightarrow A< \frac{1}{5}+\frac{1}{12}.3+\frac{1}{60}.3\\ \Rightarrow A< \frac{1}{5}+\frac{1}{4}+\frac{1}{20}\\ \Rightarrow A< \frac{4+5+1}{20}\\ \Rightarrow A< \frac{1}{2}\left(đpcm\right)\)
Chúc bạn học tốt!
Choose the word whose stress is different from the others
1. *
1 điểm
usual
pollution
section
scenic
2. *
1 điểm
revision
congestion
mountain
suggestion
3. *
1 điểm
mathematic
invitation
consideration
celebration
4. *
1 điểm
tactic
attraction
construction
connection
5. *
1 điểm
athletic
energetic
scientific
invitation
Choose the correct answer
6. We often go fishing _________ the weekend. *
1 điểm
from
while
between
during
7. Sarah and I should _________ this homework before 9.00 p.m. *
1 điểm
make
take
do
play
8. My cousins went to the movie theater yesterday, ___________. *
1 điểm
neither do I
So do I
neither did I
so did I
9. We won’t cancel our plans for you *
1 điểm
he won't too
he isn't either
neither won't he
he won't either
10. No one wants to go camping because it's raining outside. ________________. *
1 điểm
So do we
Neither do we
we too
we want either
Choose the correct Wh - question
11. _____________ did you last see him? - At the movie theater. *
1 điểm
Where
When
How
What
12. _________ does it take you to go to school every day? *
1 điểm
How far
How long
How much
How many
13. ____________ do you go on summer vacation with? - Nhan and Trang. *
1 điểm
What
When
Whom
How
14. ____________ didn't you go to school yesterday? - I was sick. *
1 điểm
How
When
What
Why
15. _________ is it from your house to the supermarket? *
1 điểm
How far
How long
How distance
How much
Bài 1 :
\(S=\frac{2}{1.2.3}+\frac{2}{2.3.4}+...+\frac{2}{2009.2010.2011}\)
\(=\frac{1}{1.2}-\frac{1}{2.3}+\frac{1}{2.3}-\frac{1}{3.4}+...+\frac{1}{2009.2010}-\frac{1}{2010.2011}\)
\(=\frac{1}{1.2}-\frac{1}{2010.2011}<\frac{1}{2}\)
Vậy \(S<\frac{1}{2}\)
Bài 2:
Làm nhiều rồi vào trong chỗ góc học tập của tớ mà coi 
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