Is $q(n)=1/n$ a negligible function? By definition - $q(n)$ is a negligible function if for every positive integer $c&gt;0$ there exist an integer $N_c$ such that for all $x&gt;N_c$  :


$q(n)&lt;1/x^c$


So for the function $1/x$, if we take the positive integer $c=1$ then we need to find some $N_c$ such that for every $x&gt;N_c$:


$1/x&lt;1/x$


$=&gt;$ Definitely such $N_c$ does not exist then $1/x$ is not a negligible function.

Is that sufficient?
Yes, that is sufficient.



I realise this isn't the most helpful of answers, but I'm not quite sure how we're supposed to deal with questions that lend themselves so neatly to one word answers. Certainly it seems wrong that something that has been solved should continue to sit in the 'unanswered questions' column!