I am not sure how to go about doing this, I know that:
$$O(g(n))=\{f : \exists \ c \ \in \Bbb R_+, \ \exists \ n_0 \in \Bbb N, \ \forall \ n\geq n_0 :f(n) \le c·g(n)\},$$
but how do I go about using this to prove the statement?
Thanks for any help!