Sequence {a n} = n-3 / 2n + 1, try to judge whether 2 / 11, 8 / 25 are the items in the sequence, if so, what is the item?

Sequence {a n} = n-3 / 2n + 1, try to judge whether 2 / 11, 8 / 25 are the items in the sequence, if so, what is the item?

Let's assume that the term is one of them and we get two equations
The first equation n = 5, the second equation has no solution
Answer 2 / 11 is the fifth item in the sequence, and 8 / 25 is not one of them

What is the maximum value of sequence ((2n + 1) (9 / 10) n power

Let f (x) = (2x + 1) (9 / 10) ^ x (x > 0) be derivative of F (x): [f (x)] '= 2 (9 / 10) ^ x + ln (9 / 10) (2x + 1) (9 / 10) ^ X and [f (x)]' = 0, then the function f (x) has extremum at x = 8.99122... And the second derivative of F (x): [f (x)] '= 2ln (9 / 10) (9 / 10) ^ x + ln (9 / 1)

Find the sequence 0,1,1,3,5,11,21 The general term formula of

a1=0
a2=1
a(n+1)=2a(n-1)+an

If S2 = 2, S4 = 10, then S6 equals ()
A. 12B. 18C. 24D. 42

The sum of the first n terms of ∵ arithmetic sequence {an} is SN. S2, s4-s2 and s6-s4 form arithmetic sequence, that is, 2, 8 and s6-10 form arithmetic sequence, 2 + s6-10 = 8 × 2 and S6 = 24, so C is selected

If S2 = 2, S4 = 10, then S6 equals ()
A. 12B. 18C. 24D. 42

The sum of the first n terms of ∵ arithmetic sequence {an} is SN. S2, s4-s2 and s6-s4 form arithmetic sequence, that is, 2, 8 and s6-10 form arithmetic sequence, 2 + s6-10 = 8 × 2 and S6 = 24, so C is selected

If S2 = 2 and S6 = 24, then S4 is equal to SN

Because the sequence {an} is an arithmetic sequence,
So S2, s4-s2, s6-s4 are also arithmetic sequences,
So S2 + s6-s4 = 2 (s4-s2),
The solution is S4 = (3s2 + S6) / 3 = (6 + 24) / 3 = 10

Note that the sum of the first n terms of the arithmetic sequence {an} is Sn, if A1 = 12, S4 = 20, then S6=______ ．

The sum of the first n terms of ∵ arithmetic sequence {an} is Sn, A1 = 12, S4 = 20, ∵ A4 + A1 = 10, ∵ A4 = 192, ∵ d = 3, ∵ S6 = 6 × 12 + 6 × 52 × 3 = 48, so the answer is: 48

Let the sum of the first n terms of the arithmetic sequence {an} be Sn, S4 = - 62, S6 = - 75, and find ︱ a1 + ︱ A2 + ︱ A3 + +︳a1

S4 = 4A1 + (4x3) / 2D = - 62s6 = 6A1 + (6X5) / 2D = - 75D = 3, A1 = - 20  an = a1 + (n-1) d = 3n-23, from an > 0, that is, 3n-23 > 0 to n > 23 / 3, so when N0; let tn be the first n term of {an} and when n = 8, TN = | A1 | + | A2 | + | A3 | + +|a7|+|a8|+… +|an|=-a1-a2-a3-… -a7+a8+… +an=Sn...

The sequence {an} is an arithmetic sequence, the sum of its first n terms is Sn, and the values of S4 = - 62, S6 = - 75, A1 ︱ + A2 ︱ +... + A14 ︱

When S4 = 4A1 + 6D = - 62s6 = 6A1 + 15d = - 75a1 = - 20, d = 3an = a1 + (n-1) d = 3n-23n ＜ 8, an ＜ 0n ≥ 8, an ＞ 0 | A1 | + | A2 | + +|a14|= -(a1+a2+a3+a4+a5+a6+a7) +a8+a9+a10+a11+a12+a13+a14= -S7+(S14-S7)=-2S7+S14=147

If A2 + A6 + A7 = 18, then the value of S9 is ()
A. 64b. 72C. 54d. None of the above is true

According to the meaning of the title, 3A1 + 12D = 18, that is, a1 + 4D = 6, that is, A5 = 6  S9 = (a1 + A9) × 92 = 2a5 × & nbsp; 92 = 54, so C