Tính được các giới hạn sau, khi đó: a) lim ( √ 3 )^ n = − ∞

a) Sai

b) Sai

c) Đúng

d) Đúng

 

a) \(\lim {(\sqrt 3 )^n} = + \infty (\)do \(\sqrt 3 > 1)\)

b) \(\lim {\pi ^n} = + \infty (\) do \(\pi > 1)\)

c) \(\lim \left( {{n^3} + 2{n^2} - 4} \right) = \lim {n^3} \cdot \left( {1 + \frac{2}{n} - \frac{4}{{{n^3}}}} \right) = + \infty \).

Vì \(\left\{ {\begin{array}{*{20}{l}}{\lim {n^3} = + \infty }\\{\lim \left( {1 + \frac{2}{n} - \frac{4}{{{n^3}}}} \right) = 1 > 0}\end{array}} \right.\)

d) \(\lim \left( { - {n^4} + 5{n^3} - 4n} \right) = \lim {n^4} \cdot \left( { - 1 + \frac{5}{n} - \frac{4}{{{n^3}}}} \right) = - \infty \).

Vì \(\left\{ {\begin{array}{*{20}{l}}{\lim {n^4} = + \infty }\\{\lim \left( { - 1 + \frac{5}{n} - \frac{4}{{{n^3}}}} \right) = - 1 < 0}\end{array}} \right.\)