Respuesta :
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
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