Tính các giới hạn sau:
1) lim\frac{3x^2}{2x+1}\frac{(2x-1)(3x^2+x+1)}{4x^2} 2)\mathop {\lim }\limits_{x \to -\infty }\frac{x+\sqrt{x^2+2}}{\sqrt{8x^2+5x+2}}
3) \mathop {\lim }\limits_{x \to +\infty }\frac{(2x-3)^2(4x+7)^3}{(3x^2+1)(10x^2+9)} 4) \mathop {\lim }\limits_{x \to -\infty }\frac{\sqrt{x^2+2x}+3x}{\sqrt{4x^2+1}-x+2}
5) \mathop {\lim }\limits_{x \to -\infty }\frac{(x-1)(x-2)(x-3)(x-4)(x-5)}{(5x-1)^5}
6) \mathop {\lim }\limits_{x \to -\infty }\frac{\sqrt{2x^4+x^2-1}}{1-2x} 7) \mathop {\lim }\limits_{x \to +\infty }\frac{x+\sqrt{x^2+1}}{2x+\sqrt{x+1}}
8) \mathop {\lim }\limits_{x \to -\infty } \frac{2x^2+x-1}{x\sqrt{x^2-1}}