Originally Posted by

**jj451** I'm struggling with the following sum:

$\displaystyle \displaystyle\sum\limits_{n=0}^{N+1} \frac{1}{x^n}$

I've tried using a geometric series with the nth term equaling $\displaystyle ar^{n-1}$ where $\displaystyle a,r = \frac{1}{x}$, and using the geometric sum of the first N+2 terms:

$\displaystyle S_{N+2} = \frac{1-\frac{1}{x^{N+2}}}{x-1}$

but I don't think thats correct. I just checked in Wolfram Alpha and the answer there is mine multiplied by $\displaystyle x$ so I'm probably just missing something simple.

Not really sure what to do really so any help would be appreciated.