Đáp án + Giải thích các bước giải:
`S=1+2+5+14+...+(3^(n-1) +1)/(2)`
`S=2/2+4/2+10/2+...+(3^(n-1) +1)/(2)`
`S=(3^0+1)/2+(3^1+1)/2+(3^2+1)/2+...+(3^(n-1) +1)/(2)`
`S=(3^0)/2+1/2+(3^1)/2+1/2+(3^2)/2+1/2+...+(3^(n-1))/(2)+1/2`
`S=1/2.n+1/2(3^0+3^1+3^2+...+3^(n-1))`
`S=1/2.n+1/2. (3^(n-1))/2`
`S=n/2+ (3^(n-1))/4`
`S=(3^n+2n-1)/4`
`S = 1 + 2 + 5 + 14 +.....+(3^(n-1)+1)/2`
`⇔2S= 2 +4+ 10+ 28+.....+(3^(n-1)+1)`
`⇔2S=(1+3+9+27+...+3^(n-1))+(1+1+...+n) ` `(có n số 1)`
`⇔2S=2n+(3+9+27+...+3^n)/3`
`⇔2S=2n+(3^n-1)/2`
`⇔S=n+(3^n-1)/4`
`⇔S=(3^n+4n-1)/4`
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Một mảnh bìa hình thang có diện tích 60 M2, chiều cao 6cm, đáy lớn hơn đáy bé 4cm. Nếu đáy lớn giảm 4cm và giữ nguyên đáy bé thì diện tích mảnh bìa là bao nhiêu xăng-ti-mét vuông?
III. Mark the letter A, B, C or D to indicate the correct answer to each of the following question. 5.My mom …………….me if she knew the truth A. would punish B. had punished C. will punish D. would had punished 6.She has to pay for the bill , …………..? A. hasn’t she B. didn’t she C. does not she D. doesn’t she 7 The local government suggested …………a road through the Nam Cat Tien national Park A. build B. built C. building D. to build 8.It is difficult …………..us to persuade him to believe what we said A. to B. for C. in D. about 9.It is necessary to be …………..of the danger of air pollution A. thinkable B. aware C. believable D. knowledgeable 10.Would you mind if I ……..your cell phone? A. using B. use C. used D. will use 11. A lot of ……were built to solve the traffic jam problem at intersections A. flyovers B. trams C. skytrains D. tunnels 12. The very first metro is being built to …….the travel demands of Saigonese A. take B. give C. solve D. meet 13.I would like to meet the man to…………I talked at the meeting last week A. who B. whom C. that D. which 14. I think the life today is …………..comfortable than it was in the past A. about as B. a lot more C. more and more D. the more 15. ……….solve the traffic problems in our city, we need to promote the development of public transport A. so that B. because of C. although D. in order to V. Mark the letter A, B, C or D to indicate the correct response to each of the following exchanges 19.”What a meaningful thing you’ve done for your less fortunate friends, my son” “………..” A. Thanks for taking care of me, mom B. What a meaningful gift you’ve made for me C. I don’t really care. I must go now D. Thank you mom that’s just a bit I can do for them 20.Lora: “ New year is coming, I’ll repaint the house for Mrs. Poor Old Amada” Jane: “____________” A. No, not for me B. That would be great help C. It must be very expensive D. Not at all VI. Mark the letter A, B, C or D to indicate the word(s) CLOSEST in meaning to the underlined word(s) in each of the following questions. 21.Due to the changes in the economic situation, many factories has to close down A. reject B. stop doing business C. cut back on D. rebuild 22.I am sure that he will win the best actor award this year A. medal B. trophy C. income D. prize
Viết số thập phân 9 ,125 thành hỗn số
Chọn từ có phát âm khác: 1) A. banana B. favourite C. famous D. grade 2) A. equation B. collection C. dictionary D. direction 3) A. racks B. comics C.maps D. novels 4) A. concert B. scout C. score D. calendar
Các bạn chỉ cần chỉ cho mink câu 4 thôi nha
Giúp mình nha. Đúng và nhanh nha!
Ai giúp mình bài này với !!!!!!!
Vẽ Chibi hoặc Anime Kí nha kẻo bị Kick câu trả lời
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