Answer :

HarleyQuinn619
the answer is -143231 
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Answer:

−143231

Explanation:

The general term of a geometric series can be described by the formula:

an=arn−1

where the initial term is a and common ratio r.

Then we find:

(1−r)N∑n=1an=N∑n=1arn−1−rN∑n=1arn−1=a+N∑n=2arn−1−N∑n=2arn−1−arN=a(1−rN)

So dividing both ends by (1−r) we find:

N∑n=1an=a(1−rN)1−r

In our example, N=7, a=−11 and r=−5

So:

7∑n=1(−11)(−5)n−1=

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