$\begin{aligned} \lim _{x \rightarrow \infty}(1-&\left.\frac{4}{x-1}\right)^{3 x-1} \\ &=e^{\lim _{x \rightarrow \infty}}\left(\frac{-4}{x-1}\right)\left(1^{\infty} \text { form] }\right.\\ &=e^{\lim _{x \rightarrow \infty}-\frac{12 x+4}{x-1}}=e^{-12} \end{aligned}$