SOLUTION: Find a formula for Sn the sum of the first n terms of the sequence 25,-5,5......

Question 882108: Find a formula for Sn the sum of the first n terms of the sequence 25,-5,5......
Answer by richwmiller(17219) (Show Source): You can put this solution on YOUR website!
This is neither arithmetic nor geometric.
25 -30 40
-5 10 40
5 50
55
The fourth term is 55
Term n =Tn
Tn=20*x^2-90*x+95
1 25 25
2 -5 20
3 5 25
4 55 80
5 145 225
6 275 500
7 445 945
8 655 1600
9 905 2505
10 1195 3700
11 1525 5225
12 1895 7120
13 2305 9425
14 2755 12180
15 3245 15425
16 3775 19200
17 4345 23545
18 4955 28500
19 5605 34105
20 6295 40400

RELATED QUESTIONS
The sum of the first n terms of an arithmetic squence is given by the formula; Sn= n/2... (answered by edjones)

the sum of the first n terms,Sn of a series is given by Sn=2n*2/(n*n)+1,then is the... (answered by Fombitz)

The first term of an infinite geometric sequence is 4. The sum of the infinite sequence... (answered by Edwin McCravy)

Find the partial sum Sn of the geometric sequence that satisfies the given conditions. a (answered by ikleyn)

find n for the given sum of Sn 34+31+28+25+22+... Sn=... (answered by tommyt3rd)

for part (a) find the sum of the first n terms of the arithmetic series. for part (b)... (answered by mathstutor458,KMST)

Given the formula f(n) = 3(-1)n find the first 5 terms of this... (answered by fractalier)

Use the formula for the sum of the first n terms of a geometric sequence. find the sum... (answered by ewatrrr)

The sum n terms is given by sn=n/2(1+n) find the fifth term of the... (answered by ewatrrr)