I have to solve the following $n^2+n \in O(n^2−n)$.
I did it this way: $n^2+n \in O(n^2−n) = n^2 \in O(n^2−n) = n^2 / n^2-n = 2n / 2n-n$ which is infinite.
I don't know if this is correct because the $-n$ in the $O$ notation is confusing me and I haven't found anything about it online. I know if this would be at example -1000 that $n^2+n \in O(n^2−n)$ would be correct.
Could someone explain it to me ?