We're given $f(n)=\frac{1}{5}n^2-30n-5$ and $g(n)=n^2$, and are asked to prove $f \in \Omega(g)$. The exercise was posted, but no solution is given (this is not an assignment question).
So by looking at it, I understand that both are $n^2$ so it should be true, but I can't figure it out. For reference, we use this to prove: $\exists c \in \mathbb{R}^+, \exists B \in \mathbb{N}, \forall n \in \mathbb{N}, n \geq B \implies f(n) \geq cg(n)$.
Obviously (?) if we choose a small enough value of $c$, then it'll make $g(n)$ negligible, but how do we just choose it?