# Is $3^{2n}$ geometric, if so find common ratio and sum or the first n terms?

$3^{2n}$ is it arithmetic or geometric, or neither. If arithmetic find common difference and sum of first n terms. If geometric, find common ratio and sum of first n terms.

• Try looking at the first three elements to find which it might be... – Thomas Andrews Mar 14 '13 at 19:21

Hint: $3^{2n} = (3^2)^n = 9^n$.
$$\sum_{k=1}^n r^k =\frac{r \left(r^n-1\right)}{r-1}$$