+525 What is the sum of the first 7 terms of the series −8+16−32+64−... ?
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
