Tìm các giới hạn:
1> lim \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}