diff --git a/编写小组/试卷/0103高数模拟试卷.md b/编写小组/试卷/0103高数模拟试卷.md index 26ccfb7..f4cca66 100644 --- a/编写小组/试卷/0103高数模拟试卷.md +++ b/编写小组/试卷/0103高数模拟试卷.md @@ -190,7 +190,7 @@ $$\begin{aligned}\lim_{x \to 3a} \frac{f(x)}{x-3a} &= \lim_{x \to 3a} \frac{\fra **答案**:$\displaystyle \lim_{x \to 3a} \frac{f(x)}{x-3a} = -\frac{1}{2}$. 若级数$\sum\limits_{n=1}^{\infty}\frac{n^p}{(-1)^n}\sin(\frac{1}{\sqrt{n}})$绝对收敛,则常数$p$的取值范围是$\underline{\quad\quad\quad}.$ - 首先,考虑级数$\sum\limits_{n=1}^{\infty}|\frac{n^p}{(-1)^n}\sin(\frac{1}{\sqrt{n}})|=\sum\limits_{n=1}^{\infty}\frac{n^p}{(-1)^n}|\sin(\frac{1}{\sqrt{n}})|$ + 首先,考虑级数$\sum\limits_{n=1}^{\infty}|\frac{n^p}{(-1)^n}\sin(\frac{1}{\sqrt{n}})|=\sum\limits_{n=1}^{\infty}{n^p}|\sin(\frac{1}{\sqrt{n}})|$ 当$n\to\infty$时,$\frac{1}{\sqrt{n}}\to 0$,此时有等价无穷小关系:$\sin(\frac{1}{\sqrt{n}}) \sim \frac{1}{\sqrt{n}}.$ 因此,级数的通项可以近似为$\frac{1}{n^p}\frac{1}{\sqrt{n}}=\frac{1}{n^{p+\frac{1}{2}}}$ 根据**p级数**的收敛性结论,级数$\sum\limits_{n=1}^{\infty}\frac{1}{n^{p+\frac{1}{2}}}$当且仅当$p+\frac{1}{2}>1$时收敛,即$p>\frac{1}{2}$,