12.21 13.41 25.81 38.161 () what's in brackets? RT I got it. 63.321 Experts help me identify, right?

RELATED INFORMATIONS

• 1. Observe the sequence 6, 7, 9, 13, 21, then fill in the rule on the horizontal line (that is, the next number)
• 2. 1. All odd numbers except 1 are grouped by one, two, three and four circulations: (3), (5,7), (9,11,13), (15,17,19,21), (23), (25,27), (29,31,33), (35,37,39,41), (43),. Then, what are the numbers in the brackets in 2011?
• 3. 1. What's the rule of 5, 17, 49? It's about sequence
• 4. Find sequence 1 / 2, 3 / 4, 5 / 8, 16 / 17 The sum of the first n terms of 2N-1 / 2 ^ n Sn = 1×1/2 + 3×1/4 + 5×1/8 + ...+ (2n-3)/2^(n-1) + (2n-1)/2^n Sn/2 = 1×1/4 + 3×1/8 + 5×1/16 + ...+ (2n-3)/2^n + 2n-1/2^(n+1) Sn - Sn/2 = 1/2 - 1 + 2( 1/2 + 1/4 + 1/8 + ...+ 1/2^n ) - 2n-1/2^(n+1) Sn = -1/2 + 2×(1/2)×(1-1/2^n)/(1-1/2) - 2n-1/2^(n+1) = 3 - (2n+3)/2^n Why is the third step Sn - Sn / 2 = 1 / 2 - 1... Where does this - 1 come from?
• 5. A multiple choice question related to sequence If we know that a, B and C are in equal proportion sequence, M is the median of a and B, and N is the median of B and C, then (A / M) + (C / N) is equal to A.1 B.2 C.1/2 D.1/4 Please give me a detailed derivation process or solution, or you can chat with me alone. If the idea is clear and easy to understand, I will add scores,
• 6. If A1 = 1, then S4 = () A. 7B. 8C. 15D. 16
• 7. If A1, A2,..., a8 are arithmetic sequences with all items greater than zero and the tolerance D is not equal to 0, then () a a1a8 > a4a5 B a1a8a4 + A5 D a1a8 = a4a5 If the general term of {an} is an = 2n + 1, then the sum of the first n terms of {BN} determined by BN = (a1 + A2 +. + an) / N (n belongs to positive integer) is () a n (n + 1) B N (n + 1) / 2 c n (n + 5) / 2 D n (n + 7) / 2
• 8. Sequence 6, 24, 60120, (how to fill in brackets?
• 9. Write the general term formula. (1) 1 / 2; 3 / 4; 5 / 6; 7 / 8;... (2) 3; 5; 9; 17; 33... (3) 6; 66; 666; 6666... (4) 1,2,4,3,8,4,16 Write the general formula (1)1/2;3/4;5/6;7/8;... (2)3;5;9;17;33... (3)6;66;666;6666... (4)1,2,2,4,3,8,4,16,5... (5)-1,1,-1,1,-1,1...
• 10. 3,18,60,147,( Such as the title
• 11. 4 12 24 40 60 according to what rules
• 12. Find the first n terms and S N of sequence 1 * 2 / 2,2 * 3 / 2,3 * 4 / 2,4 * 5 / 2
• 13. 1. Sequence: 1, - 2,3, - 4 What is the sum of the first 99 items of (- 1) ^ (n-1)? 2. Equal ratio sequence 1, A1, A2, A3 Then A1 * A2 * A3 * *a2n=?
• 14. Sequence - 1,3, - 2, - 4,11, ()
• 15. 1. Fibonacci sequence is 1, 1, 2, 3, 5, 8, 13 What is the difference between the 100th term and the sum of the first 98 terms 2. There are two gears meshing with each other as shown in the figure. A straight line with an arrow is drawn on each gear. At the beginning, the two arrows are just opposite. Then the small wheel rotates clockwise. If the big wheel has 177 teeth, the two arrows meet again after the small wheel rotates
• 16. The following equations can be obtained by calculation: 22-12 = 2 × 1 + 1, 32-22 = 2 × 2 + 1, 42-32 = 2 × 3 + 1,..., (n + 1) 2-n2 = 2 × n + 1. Add the above equations to get: (n + 1) 2-12 = 2 × (1 + 2 + 3 +...) +n) 1 + 2 + 3 + +N = n (n + 1) 2 analogy above: please find 12 + 22 + 32 + +The value of N2 (it is required that there must be an operational reasoning process)
• 17. Sequence: 2,4,7,11,16,22,29 Then the general term an =?
• 18. What kind of function or sequence is 1,2,4,7,11,16,22,29? Who can use an equation to express the increasing relationship?
• 19. The circumference of a rectangle is 88cm, and the ratio of length to width is 7 to 4. How many centimeters are the length and width of the rectangle? How many square centimeters is the area? In order to support the drought stricken areas in Southwest China, the school carried out the theme activity of "love for drought stricken areas". The students collected waste mineral water bottles and donated the money to the disaster area. The students of class 62 were divided into three groups to collect mineral water bottles. The ratio of the number of bottles collected by the first group and the second group was 4:3, The ratio of the number of bottles collected by the second group and the third group is 6:5. What is the ratio of the number of bottles collected by the three groups?
• 20. 69 10 One day, Uncle Li works 4 hours in the morning and 3 hours in the afternoon, processing 1400 parts. If Uncle Li's work efficiency remains unchanged, how many parts does he process in the morning?