Giải thích các bước giải:
Ta có:
\(\begin{array}{l}
\lim \frac{{a{n^3} + b{n^2} + n - 5}}{{\left( {a + 2b} \right){n^3} - 4{n^2} + 10n + 1}}\\
= \lim \frac{{a + \frac{b}{n} + \frac{1}{{{n^2}}} - \frac{5}{{{n^3}}}}}{{\left( {a + 2b} \right) - \frac{4}{n} + \frac{{10}}{{{n^2}}} + \frac{1}{{{n^3}}}}}\\
= \frac{a}{{a + 2b}}\\
\Rightarrow \frac{a}{{a + 2b}} = 0 \Leftrightarrow \left\{ \begin{array}{l}
a = 0\\
b \ne 0
\end{array} \right.
\end{array}\)
