5+(-5/2)+(5/4)

Question

Sn=189

Find n for the given sum if the geometric series

Answer 1

looks like
a = 5 and r = -1/2

so 5((1 - (-1/2)^n)/(1-(-1/2)) = 189
1 - (-1/2)^n = 56.7
(-1/2)^n = -56.7

since we know that n must be a whole number and for the above to be true, n must be odd
so we could solve
(1/2)^n = 56.7
using logs,

n = log 56.7/log .5 = a negative
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