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Câu hỏi: Tính ${\mathop {\lim }\limits_{x \to - \infty } \left( {{x^3} + 3x + 1} \right)}$
A. ${ + \infty }$.
B. ${1}$.
C. ${2}$.
D. ${ - \infty }$.
A. ${ + \infty }$.
B. ${1}$.
C. ${2}$.
D. ${ - \infty }$.
Ta có: $\underset{x\to -\infty }{\mathop{\lim }} \left( {{x}^{3}}+3x+1 \right)=\underset{x\to -\infty }{\mathop{\lim }} {{x}^{3}}.\left( 1+\dfrac{3}{{{x}^{2}}}+\dfrac{1}{{{x}^{3}}} \right)=-\infty .\left( 1+0+0 \right)=-\infty $
Đáp án D.