# Sum of series

Determine the 6-th member and the sum of a geometric series:

5-4/1+16/5-64/25+256/125-1024/625+....

Correct result:

a6 =  -1.64
SUM =  2.78

#### Solution:

$S=\frac{{a}_{1}}{1-q}=\frac{25}{9}=2.78$

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