Show that $$f_n: \mathbb{R} \rightarrow \mathbb{R}; \ n\ge1; \ f_n (x)=\frac{x \sqrt{n}}{n \sqrt{n}+x^2}$$ does not converge uniformly on $\mathbb{R}$
I have showed that $f_n(x)$ pointwise converges to $0$.
Then I find the maximum of $|f_n(x)|$ and it is for $x=n^{3/4}$ and $x=-n^{3/4}$
Hence $\sup_{\mathbb{R}}{|f_n(x)|}=f_n(n^{3/4})=\dfrac{1}{2 n^{1/4}} \rightarrow 0$
Where is the mistake?