SOLUTION: what is the sum of the first five terms using the geometric series formula for the sequence {1/2, -1, 2, -4,...}, sequences stump me. Thanks!

Question 1160250: what is the sum of the first five terms using the geometric series formula for the sequence {1/2, -1, 2, -4,...}, sequences stump me. Thanks!
Answer by mananth(16946) (Show Source): You can put this solution on YOUR website!
what is the sum of the first five terms using the geometric series formula for the sequence {1/2, -1, 2, -4, 8...},
To find
S(5)
we use formula

a1=1/2 , r=−2 , n=5
. After substituting these values to above formula, we obtain:

S5 = (1/2) * 11
=5.5

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