Chọn kết quả sai trong các giới hạn dưới đây:

* Hướng dẫn giải

\(\begin{array}{l} + )\,\,\lim \frac{{{{5.4}^n} + {{7.2}^n} - {3^n}}}{{{{4.4}^n} - {{2.3}^n}}}\\ = \lim \frac{{5 + 7.{{\left( {\frac{2}{4}} \right)}^n} - {{\left( {\frac{3}{4}} \right)}^n}}}{{4 - 2{{\left( {\frac{3}{4}} \right)}^n}}} = \frac{5}{4}\\ + )\,\,\lim \frac{{\sqrt {9{n^2} + 4}  - n}}{{{n^2}}}\\ = \lim \frac{{\sqrt {\frac{9}{{{n^2}}} + \frac{4}{{{n^4}}}}  - \frac{1}{n}}}{1} = 0\\ + )\,\,\lim \frac{{{3^n} + {{4.5}^n} - {8^n}}}{{{{3.8}^n} + {{2.6}^n}}}\\ = \lim \frac{{{{\left( {\frac{3}{8}} \right)}^n} + 4{{\left( {\frac{5}{8}} \right)}^n} - 1}}{{3 + 2{{\left( {\frac{6}{8}} \right)}^n}}}\\ =  - \frac{1}{3}\\ + )\,\,\lim \frac{{\sqrt {{n^2} + 4}  + n}}{n}\\ = \lim \frac{{\sqrt {1 + \frac{4}{{{n^2}}}}  + 1}}{1} = 1\end{array}\)