Question

help plz

Answer 1

\[\sum_{n=1}^{7}2(-2) ^{n-1}\]

Answer 2

you can use a formula, but it might be easier just to add

Answer 3

first off \[\sum_{n=1}^{7}2(-2) ^{n-1}=2\sum_{n=1}^{7}(-2) ^{n-1}\]

Answer 4

you need to compute \[\sum_{n=1}^{7}(-2) ^{n-1}\] and then multiply the result by \(2\)

Answer 5

is there a way to put that in a calculator

Answer 6

i can put it in wolfram but the formula you want to use is \[\sum_{n=1}^7(-2)^{n-1}=\frac{(-2)^7-1}{-2-1}\]

Answer 7

you get
\[\frac{-128-1}{-3}=\frac{127}{3}=43\] then multiply the result by \(2\) and get \(86\)

Answer 8

if you want to use a calculator for the entire thing, just type it in as you typed in in here in to wolfram and out it will pop
http://www.wolframalpha.com/input/?i= \sum_{n%3D1}^{7}2%28-2%29+^{n-1}

Answer 9

Thank you @satellite73