Untitled

I don’t really understand the limit.

A way to use Stolz is to take the logarithm.

$\log a_n - \log a_{n-1}= \log \frac{a_n}{a_{n-1}}$. In case $\frac{a_n}{a_{n-1}}$ has a limit, the limit of $a_n - a_{n-1}$ can be computed.