Find the interval of all values for X for which the series

summation of n=1 to infinity 5^(n)x^(n) converges

1.[-1/5,1/5]
2.(0,5)
3.(-1/5,1/5)
4.[0,1/5]
5.(-5,5)
5.[-5,5]

3:

(5^n)(1/5^n) = (5^n)(5^-n) = 5^(n-n) = 1 ... so, sum diverges for x=1/5

three seems like the only choice to make sense, x=5 cannot work