Tìm các giới hạn:
1> $\mathop {\lim }\limits_{x \to +\infty }$ $\frac{x^3 -5}{x^2 + 1}$ 2> $\mathop {\lim }\limits_{x \to -\infty }$$\frac{\sqrt{x^4 - x}}{1-2x}$
3> $\mathop {\lim }\limits_{x \to -\infty }$$\frac{2x^4 - x - 1}{x^2 + x + 1}$
4> $\mathop {\lim }\limits_{x \to -\infty }$ $\frac{x^2 - 5x + 2}{2\left| {x} \right| +1}$ 5> $\mathop {\lim }\limits_{x \to- \infty } $$\frac{1}{2x^3 - x^2 + 3x + 5}$