Ta có: \(\mathop {\lim }\limits_{x \to {1^ - }} ( - 3x - 1) = - 4 < 0\)
\(\left\{ \matrix{
x - 1 < 0,\forall x < 1 \hfill \cr
\mathop {\lim }\limits_{x \to {1^ - }} (x - 1) = 0 \hfill \cr} \right. \Rightarrow \lim {{ - 3x - 1} \over {x - 1}} = + \infty \)
Chọn đáp án D.
