The sequence {an} has k terms, the first n terms and Sn = 2n ^ 2 + n (n ∈ [1, k], n is a positive integer) Now we extract a term that is not the first term but not the last term. The average value of the remaining k-1 is 79 (1) Find an (2) Find K, and find out which term is the extraction

The sequence {an} has k terms, the first n terms and Sn = 2n ^ 2 + n (n ∈ [1, k], n is a positive integer) Now we extract a term that is not the first term but not the last term. The average value of the remaining k-1 is 79 (1) Find an (2) Find K, and find out which term is the extraction

an=sn-s（n-1）=4n-1
A1 = S1 = 2 * 2-1 = 3
∴an=4n-1
two
2k^2+k=79(k-1)+an
2k∧2+k=79（k-1）+4n-1
Reduction, n = (K Λ 2-39k + 40) / 2
N is an integer, k = 39 I have a good idea, too
n=20

Given the first n terms of sequence {an} and Sn = 3N + K (k is a constant), then the following conclusion is correct ()
A. When k is any real number, {an} is an equal ratio sequence B. k = - 1, {an} is an equal ratio sequence C. k = 0, {an} is an equal ratio sequence D. {an} cannot be an equal ratio sequence

The first n terms of ∵ sequence {an} and Sn = 3N + K (k is a constant), when A1 = S1 = 3 + kn ≥ 2, an = sn-sn-1 = 3N + k - (3n-1 + k) = 3n-3n-1 = 2 × 3n-1, when k = - 1, A1 = 2 satisfies an = 2 × 3n-1, when k = 0, A1 = 3 does not satisfy 2 × 3n-1, so B is selected

The first n terms of sequence an and the N + 1 power-k of Sn = 2 are known (where k is a constant)
(1) The general term formula of the sequence an
(2) If A1 = 2, find the first n terms and TN of the sequence Nan (the last n is the subscript)