If y=1+X+X^2+X^3........|x|<1 then x=.....?

Please solve this problem.

Assuming question reads

If y=1+X+X^2+X^3........,
given |x|<1 then x=.....?

then
y=∑x^i for i=0 to ∞

y equals a known sum where
y=(1-x^n)/(1-x)
as n->&infin, then x^n->0 for |x|<1, and
y=1/(1-x)
solve for x:
x=1-(1/y)

Advice:
Please do not paraphrase math questions because math is a subject where every word and punctuation counts.