I need help in checking that string is ascending or descending and I have problems with it. so it's my "$a_n$" $$ \sqrt {n+5} - \sqrt{n} $$
and I need to use $a_{n+1} - a_n$ or $\frac {a_n+1}{a_n}$.
EDIT: it would be something like that $$ \sqrt {n+6} - \sqrt{n+1} -\sqrt{n+5}+\sqrt{n} $$ and what's next?