Summation formula help

amaresh92
whats the summation of a^n for a>1 over summation n=0 to N
thanks.

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

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

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

DonAntonio