math

the question is find the sum of the first eight terms in the series
3-12+48-192+... is
1)-13,107
2)-21,845
3)-39,321
4)-65,535
I got that a1 is 3 and a8 was -49152. I wanted to make sure this was a geometric sequence with a r of -4 and tat the + didn't mean to add. I got that the answer was 3, -39,321. THANK YOU

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asked by sara
  1. S8 = a(r^8-1)/(r-1) = 3((-4)^8-1)/(-4-1) = -39321
    looks good

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    posted by oobleck

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