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20 November, 14:18

What is the sum of a 7 term geometric series if the first term is - 11 and the last term is - 45,056, and the common ratio is - 4?

A. - 143,231

B. - 36,047

C. 144,177

D. 716,144

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Answers (1)
  1. 20 November, 14:45
    0
    This sequence is:

    a (n) = - 11 (-4) ^ (n-1)

    The sum of the sequence is:

    s (n) = - 11 (1--4^n) / (1--4)

    s (n) = - 11 (1--4^n) / 5

    so for the first seven terms

    s (7) = - 11 (1--4^7) / 5

    s (7) = - 11 (1+16384) / 5

    s (7) = - 11 (16385) / 5

    s (7) = - 36047 B.
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