Prove by induction $n! > n^2$
I am trying to prove the inequality in the title for $n\geq 4$; however, I am stuck on the induction step! Any help would be appreciated.
For $n\ge 4$, prove that $n! > n^2$.
Base Case: $n=4$, LHS $4! = 24$, RHS = $4^2 = 16$
$24>16$ : True
Induction Hypothesis: Assume True for $n=k$.
$k! > k^2$
Induction Step: Should be True for $n=k+1$
$(k+1)! > (k+1)^2$
$(k+1) . (k)! > (k^2 + 2k + 1)$
However, here is where I get stuck.
Hint:
$$(k+1)!> (k+1)^2$$ can be rewritten as
$$(k+1)\cdot (k!) > (k+1)\cdot(k+1)$$
For the induction step, here is the key part: \begin{align} (k+1)! &= (k+1)\cdot k!\tag{by definition}\\[0.5em] &> (k+1)\cdot k^2\tag{by the inductive hypothesis}\\[0.5em] &= k^3+k^2\tag{expand}\\[0.5em] &> k^2+2k+1\tag{since $k\geq 4$}\\[0.5em] &= (k+1)^2. \end{align} The main problem is realizing that you can deduce that $k^3+k^2>k^2+2k+1$ from the fact that $k\geq 4$.