Series problem (1 Viewer)

[red802]

Evaluate 2+10+50 .... 6250

can someone show me how to do that, it using geometrical stuff , (show working out)

 

[Mc_Meaney]

what is your question? are you trying to find the sum, or the number of terms?

For Term:
Tn = ar^n-1
6250= 2.5^n-1
3125= 5^n-1
5⁵= 5^n-1
therefore n=6, so it is the 5th term.

 

[SoulSearcher]

This is if you are finding the sum of the terms
r = 5
a = 2
From the working provided in the above post, the number of terms is 6, therefore the sum of the geometric series is
S₆ = 2(5⁶ - 1) / (5 - 1)
= (15625 - 1) / 2
= 15624/2
= 7812

 

[red802]

the answer is 7812, , need to find sum n

 

[red802]

thanks