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If n is an integer and n > = 1, find a formula for the expression

[tex]2^n - 2^{n-1} + 2^{n-2} - 2^{n-3} + ... + (-1)^{n-1} * 2 + (-1)^n [/tex]

okay this confuses me, because I'm not sure which is the first term and which is the last term...

I figured the ratio was the following: -2

becuase if u take 2^n/[-2^(n-1)] = -2

I took the first term and divided it by the 2nd term to find the ratio or is it vice versa? by taking the 2nd term and dividing it by the first, which would give the ratio of: -1/2?

once i find the ratio, i can find the term right after the last by multiplying the ratio by the last term in this case (-1)^n is the last term, and the first term is 2^n correct?

Thanks, once i get this figured out i cna find the formual for the sum.