题目
10.lim_(xtoinfty)(sqrt[3](x^3+x^2)-xe^(1)/(x))=__.
10.$\lim_{x\to\infty}(\sqrt[3]{x^{3}+x^{2}}-xe^{\frac{1}{x}})=\_\_. $
题目解答
答案
令 $ y = \frac{1}{x} $,当 $ x \to \infty $ 时,$ y \to 0 $。原式可改写为:
$\lim_{y \to 0} \left( \sqrt[3]{\frac{1}{y^3} + \frac{1}{y^2}} - \frac{1}{y} e^y \right) = \lim_{y \to 0} \frac{1}{y} \left( \sqrt[3]{1 + y} - e^y \right).$
利用泰勒展开:
$\sqrt[3]{1 + y} \approx 1 + \frac{y}{3} - \frac{y^2}{9}, \quad e^y \approx 1 + y + \frac{y^2}{2}.$
代入得:
$\sqrt[3]{1 + y} - e^y \approx \left(1 + \frac{y}{3} - \frac{y^2}{9}\right) - \left(1 + y + \frac{y^2}{2}\right) = -\frac{2y}{3} - \frac{11y^2}{18}.$
因此:
$\lim_{y \to 0} \frac{1}{y} \left( -\frac{2y}{3} - \frac{11y^2}{18} \right) = \lim_{y \to 0} \left( -\frac{2}{3} - \frac{11y}{18} \right) = -\frac{2}{3}.$
答案: $\boxed{-\frac{2}{3}}$