Question

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

Answer 1

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

you might need a second opinion....

Answer 2

You were right! Thank you so much!^^

Answer 3

your welcome :)