Question

Find S8 for the series -2+-10+-50+-250?

Answer 1

PLEASE HELP!

Answer 2

are you looking for the 8th term or the sum of the terms up till the 8th term ?

Answer 3

the 8th term of the sequence

Answer 4

Are you sure you are not looking for the sum of the first eight terms.....because that is what " s " means ? If you were looking for the 8th term, it would say " a8" of the series. So which one is it ? S8 or a8 ?

Answer 5

could you possibly give me both answers?

Answer 6

yes...hold on...give me a moment

Answer 7

k (:

Answer 8

The 8th term is :
an = a1 * r^(n-1)
n = 8
a1 = -2
r = 5
a8 = -2 * 5^(8 - 1)
a8 = -2 * 5^7
a8 = - 2 * 78125
a8 = -156250

The sum is :
sn = (a1(1 - r^n)/(1 - r)
n = 8
a1 = -2
r = 5
s8 = (-2(1 - 5^8)/(1 - 5)
s8 = (-2(1 - 390625)/-4
s8 = (-2(-390624)/-4
s8 = 781248/-4
s8 = -195312

Answer 9

I don't know which one you need, but here is both :)

Answer 10

it was the sum! thanks! (:

Answer 11

no problem :)