kenzieeckmeo
kenzieeckmeo kenzieeckmeo
  • 26-03-2017
  • Mathematics
contestada

Evaluate 7 sigma n=1 2(-2)^n-1

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pbjgurl123
pbjgurl123 pbjgurl123
  • 26-03-2017
\[\sum_{n=1}^{7} 2(-2)^{n-1}\]
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irspow
irspow irspow
  • 26-03-2017
Okay I think you mean the sum of the first 7 terms of the geometric sequence:

a(n)=2(-2)^(n-1)

The sum of any geometric sequence is:

s(n)=a(1-r^n)/(1-r)  in this case:

s(7)=2(1--2^7)/(1-7)

s(7)=-43
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