[tex]\frac{-1}{n^2}\leq \frac{sinn}{n^2}\leq \frac{1}{n^2}\\\lim\frac{-1}{n^2}=\lim\frac{1}{n^2}=0\\\Rightarrow \lim\frac{sinn}{n^2}=0[/tex]
Tương tự: [tex]\lim\frac{cosn}{n^2}=0[/tex]
Vậy [tex]\lim\frac{3sinn+4cosn}{n^2-n+3}=\lim\frac{3\frac{sinn}{n^2}+4\frac{cosn}{n^2}}{1-\frac{1}{n}+\frac{3}{n^2}}=0[/tex]