Chọn kết quả đúng của lim x → − ∞ ( − 4 x 5 − 3 x 3 + x + 1 ) .

B

Ta có \(\mathop {\lim }\limits_{x \to  - \infty } \left( { - 4{x^5} - 3{x^3} + x + 1} \right)\)\( = \mathop {\lim }\limits_{x \to  - \infty } {x^5}\left( { - 4 - \frac{3}{{{x^2}}} + \frac{1}{{{x^4}}} + \frac{1}{{{x^5}}}} \right)\)\( =  + \infty \).

Vì \(\left\{ \begin{array}{l}\mathop {\lim }\limits_{x \to  - \infty } \left( { - 4 - \frac{3}{{{x^2}}} + \frac{1}{{{x^4}}} + \frac{1}{{{x^5}}}} \right) =  - 4 < 0\\\mathop {\lim }\limits_{x \to  - \infty } {x^5} =  - \infty \end{array} \right.\).