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katrin2010 [14]
3 years ago
5

Find S8 for the geometric series 3 + -6 + 12 + -24 +…

Mathematics
1 answer:
kirill115 [55]3 years ago
6 0
I guess you are asking to find the sum of the first 8 terms. If so, then:
Sum = a₁(1-rⁿ)/(1-r), where a₁ is the 1st term,  r=common ratio and n=number of terms:
the 1st term a₁ =3
common ratio r = - 2 (since -6/3 = - 2, and 12/-6 = - 2, etc.)

Sum = 3[(1- (-2)⁸]/(1-2) = 3(1- 256)/(1/2)
Sum = -1530

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