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