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What is the sum of the first 7 terms of the series  −8+16−32+64−... ?

 Mar 6, 2018
 #1
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This is a Geometric Series, where:

F = First term = -8

R = Common Ratio = - 2.

N =Number of terms =7. Use the formula for GS

 

S = F x (1 -R^N) / ( 1 - R)

S = -8 x (1 - (-2^7)) / (1 - (- 2))

S = -8 x (1 - (-128)) / (1 + 2)

S = -8 x (1 + 128) / 3

S = -8 x (129 / 3)

S = -8 x 43

S = - 344

 Mar 6, 2018

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