Question

Write the sum using summation notation, assuming the suggested pattern continues.

2 - 8 + 32 - 128 + ... PLEASE HELP ME

Answer 1

wait I think I got it but I'm not sure if it would be 2(-4)^n or 2(-4)^n-1

Answer 2

The common ratio is -4 right?
a = 2
r = -4
n = GOES ON FOREVER starting from 1 :)

nth term = ar^(n-1) = 2.-4^(n-1)

So summation notation would be giving the sum of all the n terms [One by one]

\[\sum_{1}^{n} 2.(-4)^(n-1)\]

Understood? :)

Answer 3

AHHHH OKAY!!! XD that;s why it would be n-1!!! I understand way more now :) thank you!!

Answer 4

:)