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HT
2
15 tháng 12 2021
a. Chu vi là \(\left(12+5\right).2=34\left(m\right)\)
Diện tích là \(12.5=60\left(m^2\right)=600000\left(cm^2\right)\)
b. Cần lát \(600000:\left(40.40\right)=375\) viên gạch
12 tháng 9 2021
\(B=2+2^2+2^3+2^4+...+2^{99}+2^{100}=2\left(1+2^2+2^3+2^4\right)+...+2^{96}\left(1+2^2+2^3+2^4\right)=2.31+2^6.31+...+2^{96}.31=31\left(2+2^6+...+2^{96}\right)⋮31\)
HT
7
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0
DX
0
18 tháng 12 2021
21. Hoa looks red. She was outdoors yesterday. Perhaps she has _______
A. flu B. sunburn C. spots D. stomachache
22. My family has decided to use _________ electricity by using more solar energy instead.
A. more B. less C. much D. fewer
23. I ............... playing board games interesting because I can play them with my friends.
A. find B. think C. say D. tell
24. Circle the word that has the underlined part pronounced differently from the others.
A. curl B. keen C. city D. cook
25. I …………….. Nha Trang when I was a child.
A. visit B. visited C. will visit D. have visited
26. He …………… to the USA so far.
A. is B. was C. will be D. has been
27. Americans eat a lot of junk food, ………….junk food causes obesity.
A. but B. and C. so D. because
28. Tim: I feel itchy and my nose is running. Doctor: ………………………..
A. Wash your hair more. B. I think you have the flu.
C. Drink more water. Eat less meat D. I think you have a stomachache.
29. Pick out the word whose main stress is placed differently from the others.
A. allergy B. headache C. temperature D. obesity
30. Choose the word that has the underlined part pronounced differently from the others.
A. cold B. curly C. ocean D. clothes
31. -“What would you like to drink now?” - “_______________.”
A. No, thanks B. Yes, please C. I like to do nothing D. Orange juice, please
32. All of us enjoy _______ to classical music.
A. listen B. listens C. listening D. listened
33. She worked very hard, _______she passed all her exams.
A. because B. and C. so D. but
35. -“ Would you like me to turn off your computer?
- “ ______________. I’ll do it myself”
A. No, thanks B. Yes, please C. Don’t do it D. Of course
18 tháng 12 2021
I. Put the verbs in the correct form.
1. I enjoy (fish) ........................fishing.......................... because it (be) ……is………….… relaxing.
2. Jane will play chess after she (finish) …………finishes………………. school.
3. What ……………does……… your mother often (do) ………do………………at weekends?
4. I think, in the future people (not play) ……………won't play…………………… individual games.
5. We find (arrange) ………arranging……………… flowers interesting because it (help) ………helps……… us relax.
6. I (not collect) ………….won't collect……………………… dolls when I grow up.
7. She often (go) ..........goes............... to the market with her mother every weekend.
8. We (visit) ...........will visit.......... Hue next month.
9. My younger sister (collect) ........collected......... dolls two years ago.
10. ..........Do........ you ever (do) ........do......... volunteer work ?
Trả lời:
\(a,\sqrt{\left(11-6\sqrt{2}\right)^2}+\sqrt{\left(11+6\sqrt{2}\right)^2}\)
\(=\left|11-6\sqrt{2}\right|+\left|11+6\sqrt{2}\right|\)
\(=11-6\sqrt{2}+11+6\sqrt{2}\)
\(=22\)
b, \(\sqrt{\left(10-4\sqrt{6}\right)^2}-\sqrt{\left(10+4\sqrt{6}\right)^2}\)
\(=\left|10-4\sqrt{6}\right|-\left|10+4\sqrt{6}\right|\)
\(=10-4\sqrt{6}-\left(10+4\sqrt{6}\right)\)
\(=10-4\sqrt{6}-10-4\sqrt{6}\)
\(=-8\sqrt{6}\)
c, \(\sqrt{\left(4-\sqrt{5}\right)^2}+\sqrt{\left(1-\sqrt{5}\right)^2}\)
\(=\left|4-\sqrt{5}\right|+\left|1-\sqrt{5}\right|\)
\(=4-\sqrt{5}+\sqrt{5}-1\)
\(=3\)
d, \(\sqrt{\left(7+\sqrt{2}\right)^2}-\sqrt{\left(1-\sqrt{2}\right)^2}\)
\(=\left|7+\sqrt{2}\right|-\left|1-\sqrt{2}\right|\)
\(=7+\sqrt{2}-\left(\sqrt{2}-1\right)\)
\(=7+\sqrt{2}-\sqrt{2}+1\)
\(=8\)
Trả lời:
Bài 2:
a, \(5\sqrt{25a^2}-25a\) với \(a\le0\)
\(=5\sqrt{\left(5a\right)^2}-25a\)
\(=5.\left|5a\right|-25a\)
\(=5.\left(-5a\right)-25a\) (vì \(a\le0\))
\(=-25a-25a=-50a\)
b, \(\sqrt{49a^2}+3a\) với \(a\ge0\)
\(=\sqrt{\left(7a\right)^2}+3a\)
\(=\left|7a\right|+3a\)
\(=7a+3a\) (vì \(a\ge0\))
\(=10a\)
c, \(\sqrt{16a^4}+6a^2\)
\(=\sqrt{\left(4a^2\right)^2}+6a^2\)
\(=\left|4a^2\right|+6a^2\)
\(=4a^2+6a^2=10a^2\)
d, \(3\sqrt{9a^6}-6a^3\) với \(a\le0\)
\(=3\sqrt{\left(3a^3\right)^2}-6a^3\)
\(=3.\left|3a^3\right|-6a^3\)
\(=3.\left(-3a^3\right)-6a^3\) (vì \(a\le0\))
\(=-9a^3-6a^3=-15a^3\)