Chọn kết quả đúng của \(\mathop {\lim }\limits_{x \to - \infty } \left( { - 4{x^5} - 3{x^3} + x + 1} \right)\).     

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

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

\( = \mathop {\lim }\limits_{x \to 3} \frac{{\left( {2x + 1} \right)\left( {\sqrt {5x + 1}  + 4} \right)}}{5} = \frac{{56}}{5} = 11,2\).

Trả lời: 11,2.