Summation formula help

1. Sep 10, 2012

amaresh92

whats the summation of a^n for a>1 over summation n=0 to N
thanks.

2. Sep 10, 2012

DonAntonio

Hint: for $\,r\neq 1\,$ a constant, we have

$$\sum_{n=0}^mr^n=\frac{r^{m+1}-1}{r-1}$$

DonAntonio

3. Sep 10, 2012

Simon Bridge

This is the sort of thing most people just look that up - do you need to work out the formula or what?