In the arithmetic sequence 3, 12, 21, 30, 39, 48 912 is the second______ The number of them

(912-3) △ 9 + 1, = 909 △ 9 + 1, = 101 + 1, = 102; so the answer is: 102

Can you find a rule to fill in? 3，12，21，30，39，48，57… (1) The 12th number is (2) 912 is the second The number of them

(1) 3 + (12-1) × 9, = 3 + 11 × 9, = 3 + 99, = 102; the 12th item is 102; (2) let the nth item be 912, then 3 + (n-1) × 9 = 912, & nbsp; (n-1) × 9 = 909, & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; n-1 = 101, & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; n = 102; 912 is item 102

Choose three different numbers from the set {1,2,3,4,..., 21}, and make these three numbers into an arithmetic sequence, which has at most one
Can you help me

Tolerance d = 1:19
D = 2: 17
D = 3:15
D = 4:13
D = 5: 11
D = 6:9
D = 7: 7
D = 8:5
D = 9:3
D = 10:1

RELATED INFORMATIONS

1. It is known that the sum of the four numbers in the arithmetic sequence is 40, and the product of the second number and the third number is 36 OK, I'll add points immediately
2. It is known that three positive numbers a, B and C satisfy a 2, B 2 and C 2 as arithmetic sequence. It is proved that 1A + B, 1A + C and 1b + C are also arithmetic sequence
3. An arithmetic sequence is composed of three numbers, the sum of the three numbers is 30, the sum of the squares of the three numbers is 960, find the three numbers
4. Known arithmetic sequence 2, 5, 8, 11. Find the number of item 599?
5. If the arithmetic sequence 5,8,11,... And 3,7,11,... Have 100 terms, then the number of terms of their same terms is___ . But I don't understand. Please tell me, ∵3(4n-1)+2≤a100=302 ∴n≤25.
6. Two arithmetic sequences 5,8,11. And 3,7,11. Have 100 items. How many items do they have in common?
7. If the sum of the first n terms of the arithmetic sequence {an} is Sn, and S4 = 20, sn-4 = 60, Sn = 120, then n=______ ．
8. Zhang Hua, a large strawberry grower, now sells 22 tons of strawberries. There are two sales channels: one is to ship strawberries to the provincial capital for direct wholesale to retailers, and the other is to retail them in the local market. After investigation and analysis, the daily sales volume and net profit per ton of these two sales channels are shown in the following table: affected by objective factors, Zhang Hua can only use one sales channel every day, and strawberries must be sold within 10 days. (1) if Some of the strawberries are shipped to the provincial capital for wholesale and the rest are sold in the local market. Please write down the functional relationship between the net profit y (yuan) of 22 tons of strawberries sold and the quantity x (tons) of strawberries transported to the provincial capital for direct wholesale and retail. (2) how to arrange the sales channels of 22 tons of strawberries so that Zhang Hua can obtain the maximum net profit Daily sales (tons) net profit per ton (yuan) provincial wholesale 4 1200 local retail 1 2000
9. In the triangle ABC, ab = AC, CD is the height on the edge AB, prove 2 ∠ BCD = ∠ a
10. As shown in the figure, ∠ ACB = 90 ° in △ ABC, make isosceles triangle △ ABC with AC as bottom edge, ad = CD = 10, make de ⊥ AC through point D, perpendicular foot is f, de and ab intersect at point E, connect CE. (1) prove: AE = CE = be; (2) if AB = 15cm, BC = 9cm, P is a point on ray De, then when DP is the value, the perimeter of △ PBC is the smallest, and calculate the perimeter of △ PBC at this time
11. Let {an} be an increasing arithmetic sequence, the sum of the first three terms is 12, and the product of the first three terms is 48, then its first term is () A. 1B. 2C. 4D. 6
12. If three numbers form an arithmetic sequence, the sum of them is equal to 12, and the product of the beginning and the end is 12, find the three numbers
13. There are eight numbers, and their average is 7.5. It is known that the average of the first five numbers is 8.8, and the average of the last four numbers is 9.5. What is the fifth number?
14. If the sixth term of an arithmetic sequence is 5 and the sum of the third term and the eighth term is 5, what is the sum of the first nine terms of the arithmetic sequence?
15. There are two groups of numbers, the average number of the first group is 12.8, the average number of the second group is 10.2, and the total average number of these two groups is 12.02. What is the ratio of the number of the first group to the number of the second group
16. What eight numbers can be inserted between 4 and 40 to make these ten numbers an arithmetic sequence?
17. There are two arithmetic sequences 2, 6, 10 , 190 and 2, 8, 14 The common terms of the two arithmetic sequences form a new sequence from small to large, and the sum of each item of the new sequence is calculated
18. There are two arithmetic sequences 2,6,10 190 and 2,8,14 A new sequence is composed of the common terms of the two arithmetic sequences from small to large, then the sum of the items of the new sequence is__________ .
19. The sum of squares of four numbers is 94. The product of the first number and the fourth number is 18 less than the product of the second number and the third number
20. If the sum of three numbers is equal to 18 and the sum of their squares is equal to 116, then the three numbers are equal______ ．

In the arithmetic sequence 3, 12, 21, 30, 39, 48 912 is the second______ The number of them