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The law of sequence 1,4,13,40121 ·
(n-th power of 3) / 2
Sequence 1.4.13.40
1 .4 .13.40.
Find the same formula!
The sum of the first n terms of an equal ratio sequence with 1 as the first term and 3 as the common ratio
I.e. (3 ^ n-1) / 2
Find 2, 222 The sum of the first n terms
an=2+20+200+…… +2*10^(n-1)
=2*(10^n-1)/(10-1)
=(2/9)*(10^n-1)
So Sn = (2 / 9) * [10 ^ 1 + 10 ^ 2 + +10^n-1-1-…… -1]
=(2/9)*[10*(10^n-1)/(10-1)-n]
=(20/81)(10^n-1)-2n/9
RELATED INFORMATIONS
- 1. What are the rules of the results of 2 * 22 * 22 222 * 222 2222 * 2222 22222 * 22222
- 2. How to calculate 2 + 22 + 222 +. 2222?
- 3. [high school sequence] do you know that three consecutive terms can be used to find the general formula of the sequence In the stem of the question, I only said that this is a sequence of positive numbers, and I also gave a formula. The first question is to find a1a2a3, and the second question is to find the general term formula. I derived A1, A2, A3. Can I use a3-a2 = a2-a1 = D or A3 / A2 = A2 / A1 = q to find the general term formula? Or should I use the formula given by the stem of the question to prove it? Although I have made the correct answer in both methods. The question is a little long. No point. Who will answer, It is known that {an} is a sequence of positive numbers, and the median of the equal difference between an and 2 is equal to the median of the equal ratio between Sn and 2. I calculate A1 = 2, A2 = 6, A3 = 10, Then the second question can be directly explained as arithmetic sequence according to a3-a2 = a2-a1 = D? How to answer the questions in the exam? I feel too confused and want to close this question
- 4. 2+22+222+2222+…… +What is 2222?
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- 8. There is a column of numbers as follows: 4, 5, 9, 14, 23. What is the number 1999?
- 9. There is a column of numbers, 2, 5, 8, 11, 14 Then 104 is the () th number in this column A. 33B. 32C. 34D. 35
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- 11. Sequence: 3, 4, 5, 7, 8, 9, 11, 12, 13, 15, 16, 17, 18, 19, 20 Is there a general term formula? If so, what is it? No 18. I have the wrong number. I'm sorry What is the value of the number 2013?
- 12. The first five terms of known sequence are 1 / 2, 5 / 4, 7 / 8, 17 / 16, 31 / 32, and its general formula is?
- 13. Find the general formula of the following sequence 1,0,1 / 3,0,1 / 5,0,1 / 7,0
- 14. “1,2,3,5,8,13,21,34,55,89,134……” This seems to be an interesting bepoche sequence in mathematics. The most important feature of this sequence is: --
- 15. "1、2、3、5、8、13、21、34、55、89、144… "This is an interesting Fibonacci series in mathematics. What is the biggest characteristic of this series?
- 16. “1,2,3,5,8,13,21,34,55,89,144…” This is an interesting Fibonacci series in mathematics What do you learn from it
- 17. Known Fibonacci sequence: 1,2,3,5,8,13,21,34,55. There are several even numbers in the first 2003 items of this sequence
- 18. 1、0、1、0、1、0、1、…… What is the general term formula of?
- 19. General formula of 0,1,0,2,0,3
- 20. Write out a general term formula of the sequence, so that the first five terms are: 11, 12, 13, 14, 15