1. $f_{n}(x)= \frac{2nx}{1+n^{2}x^{2}}$ với $0\leq x\leq 1$
2.$f_{n}(x)=xarctanx , 0< x< +\infty$
3. $f_{n}(x)=\left\{\begin{matrix} n^{2}x & 0\leq x\leq \frac{1}{n}\\ n^{2}(\frac{2}{n}-x)& \frac{1}{n}< x< \frac{2}{n}\\ 0& x\geq \frac{2}{n} \end{matrix}\right.$