So I'm trying to figure this one out, suppose this problem A.

$f(n) = n^2 - 2n$ and $g(n) = n^2$.

I want to prove that $f(n) \in \Omega(g(n))$ by showing a set of inequalities between $f(n)$ to $g(n)$ to derieve the $c > 0$ and $n\_0 > 0$.

For example, say

$f(n) = n^2 + 2n$ and $g(n) = n^2$ and $f(n) \in O(g(n))$.

Clearly, $n^2 + 2n \le n^2 + 2n^2 = 3n^2 \quad \forall n\_0>0$ Thus, if $c = 3$ and $n\_0 > 0$, we have proved $f(n) \in O(g(n))$.

How do I do this for the former problem, problem A?

Thanks.