\(\displaystyle\lim_{{x\to\pm\infty}}\;\left(1-\frac 3x\right)^{-6x}=\displaystyle\lim_{{x\to\pm\infty}}\;\left(1+\frac3{-x}\right)^{-6x}\\=\displaystyle\lim_{{x\to\pm\infty}}\;\left(1+\frac3{-x}\right)^{\frac{-x}{3}.18}=\left[\displaystyle\lim_{{x\to\pm\infty}}\;\left(1+\frac3{-x}\right)^{\frac{-x}{3}}\right]^{18}=e^{18}\)
gricha - v5427 - 22.10.14