[tex] \lim_{x \to \infty} \frac{1}{1-x}- \frac{3}{1-x^3}=
\lim_{x \to \infty} \frac{1}{1-x}-\lim_{x \to \infty} \frac{3}{1-x^3}=0-0=0
\lim_{x \to \infty} \frac{1}{1-x}= \frac{1}{1- \infty}= \frac{1}{- \infty}=0
\lim_{x \to \infty} \frac{3}{1-x^3}= \frac{3}{- \infty} =0[/tex]