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 answer:

a6 =  -1.64
SUM =  2.78

Step-by-step explanation:

 a1=51 q=45 q<1 a6=a1q61=51=51(45)5 a6=1024625=1.64
S=a11q=259=2.78



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