Prove $1+2+3+...+n<=n^2$ for all n∈N 
Prove $1+2+3+...+n<=n^2$ for all n∈N

This is what I have so far. Not sure what to do now.

Gauss’s sum formula : $$1+2+\dots +n=\frac  {n(n+1)}2$$
For $n\ge1$, we have $\frac{n (n+1)}2\le\frac  {n (n+n)}2=n^2$...
Thus we have a proof without induction,  in case you are interested. ..
