In the arithmetic sequence, the sum of the first 10 terms of - 1,2,5,8

In the arithmetic sequence, the sum of the first 10 terms of - 1,2,5,8

The tolerance is 3. Item 10 is: (- 1) + 3 * (10-1) = 26
And: (- 1 + 26) * 10 divided by 2 = 125

Finding arithmetic sequence - 1,2,5,8 The sum of the top ten items of

General term = 3n-4
Item 10 = 3 * 10-4 = 26
Sum of the first ten terms = (26-1) * 10 / 2 = 125

It is known that the second term of the arithmetic sequence {an} is 8, and the sum of the first 10 terms is 185. (1) find the general term formula of the sequence {an}; (2) take the second term, the fourth term, the eighth term from the sequence {an} , 2n In order to form a {BN} sequence, try to find the general term formula of {BN} sequence and the sum of the first n terms

Solution (1) let the first term be A1 and the tolerance be d. from the meaning of the problem, a1 + D = 810a1 + 10 × 92d = 185, the solution is A1 = 5 and d = 3. So an = 3N + 2 (2) from the problem, we can see that & nbsp; & nbsp; B1 = A2, B2 = A4, B3 = A8 bn＝a2n＝3×2n+2∴Sn＝(3×21+2)+(3×22+2)+(3×23+2)+… +(3×2n+2)=3×（2+22+23+… +2n）+2n=3×2(1−2n)1−2+2n=3×2n+1+2n-6．