x+x^2+x^3+...x^n → x(x^n - 1)/(x - 1)
CPhill: What is the difference between this sequence and the question?
∑[x^(n), n, 1, 10] = x + x^2 + x^3 + x^4 + x^5 + x^6 + x^7 + x^8 + x^9 + x^10.........etc.
this equals x/(1-x) for all -1
I think you meant to put the condition -1 < x < 1 Max; but notice your statement is only true if n is infinite.
I have been less careful these days...