Question

Найти пределы функций:
1) lim x->1
$\frac{ {x}^{4} - 1 }{2 ln(x) }$
2) lim x-> 0
$\frac{xtgx}{ \sin(3x) }$
3) lim x-> ∞
$\frac{ {x}^{3} - 2 {x}^{2} - 1 }{( {x}^{2} - 1)(x + 1) }$
4) lim x -> ∞
$\frac{ {x}^{3} + x - 2 }{ {x}^{4} - 2x + 3 }$

Answer 1

Решение во вложении:

Answer 2

$1)\; \; \lim\limits _{x \to 1}\frac{x^4-1}{2lnx}=\lim\limits _{x \to 1}\frac{(x-1)(x+1)(x^2+1)}{2ln(1+(x-1))}=\Big [\, ln(1+\alpha )\sim \alpha \; ,\; \alpha \to 0\; \Big ]=\\\\=\lim\limits _{x \to 1}\frac{(x-1)(x+1)(x^2+1)}{2\cdot (x-1)}=\lim\limits _{x \to 1}\frac{(x+1)(x^2+1)}{2}=\frac{2\cdot 2}{2}=2\\\\2)\; \; \lim\limits _{x \to 0}\frac{x\cdot tgx}{sin3x}=\Big [\; tg\alpha \sim \alpha \; ,\; \; sin\alpha \sim \alpha \; ,\; \alpha \to 0\; \Big ]=\lim\limits _{x \to 0}\frac{x\cdot x}{3x}=\\\\=\lim\limits _{x \to 0}\frac{x}{3}=\frac{0}{3}=0$

$3)\; \; \lim\limits _{x \to \infty}\frac{x^3-2x^2-1}{(x^2-1)(x+1)}=\lim\limits _{x \to \infty} \frac{x^3-2x^2+1}{x^3+x^2-x-1}=\lim\limits _{x \to \infty}\frac{1-\frac{2}{x}+\frac{1}{x^3}}{1+\frac{1}{x}-\frac{1}{x^2}-\frac{1}{x^3}}=\frac{1}{1}=1\\\\4)\; \; \lim\limits _{x \to \infty}\frac{x^3+x-2}{x^4-2x+3}= \lim\limits _{x \to \infty}\frac{\frac{1}{x}+\frac{1}{x^3}-\frac{2}{x^4}}{1-\frac{2}{x^3}+\frac{3}{x^4}}=\frac{0}{1}=0$