Question 257095: I need your help with this geometric series
a(subscript 1)=4
r=3
S (subscript n)=484
n=? Found 2 solutions by stanbon, drk:Answer by stanbon(75887) (Show Source):
You can put this solution on YOUR website! I need your help with this geometric series
a(subscript 1)=4
r=3
S (subscript n)=484
n=?
----------------------
a(1) = 4
r = 3
----
S(n) = a(1)[r^n - 1]/[r-1]
---
4[3^n -1]/[3-1] = 484
[3^n -1]/2 = 121
3^n -1 = 242
3^n = 243
3^n = 3^5
n = 5
======================
Cheers,
Stan H.
You can put this solution on YOUR website! From the given information, the formula for the nth term is
create a table to get
T(1) = 4*3^0 = 4
T(2) = 4*3^1 = 12
T(3) = 4*3^2 = 36
T(4) = 4*3^3 = 108
T(5) = 4*3^4 = 324
If we add the first 5 terms we get 484.
n = 5
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