a $\lim_{} \dfrac{n^2-2n+3}{n^2+1}$
= $\lim_{} \dfrac{1-\dfrac{2}{n}+\dfrac{3}{n^2}}{1+\dfrac{1}{n^2}}$
=$\dfrac{1-0+0}{1+0}$ =`1`
b $\lim_{} \dfrac{5n-3.2n}{3n-5n}$
= $\lim_{} \dfrac{5n-6n}{-2n}$
= $\lim_{} \dfrac{-1n}{-2n}$
= $\lim_{}\dfrac{1}{2}$
=$\dfrac{1}{2}$
hay thì xin hay nhất