在求解以下考研数学极限计算练习题时,请仔细审题,运用极限的基本性质和运算法则:
1. 计算极限:\(\lim_{x \to 0} \frac{\sin(2x) - \sin(x)}{x}\)
解答:利用三角函数的和差化积公式,得:
\[
\lim_{x \to 0} \frac{\sin(2x) - \sin(x)}{x} = \lim_{x \to 0} \frac{2\cos\left(\frac{3x}{2}\right)\sin\left(\frac{x}{2}\right)}{x}
\]
由于当\(x \to 0\)时,\(\sin\left(\frac{x}{2}\right) \approx \frac{x}{2}\),所以:
\[
\lim_{x \to 0} \frac{2\cos\left(\frac{3x}{2}\right)\sin\left(\frac{x}{2}\right)}{x} = \lim_{x \to 0} \cos\left(\frac{3x}{2}\right) = \cos(0) = 1
\]
2. 计算极限:\(\lim_{n \to \infty} \frac{n^2 + 3n}{n^2 - 2n}\)
解答:分子分母同时除以\(n^2\),得:
\[
\lim_{n \to \infty} \frac{n^2 + 3n}{n^2 - 2n} = \lim_{n \to \infty} \frac{1 + \frac{3}{n}}{1 - \frac{2}{n}} = \frac{1 + 0}{1 - 0} = 1
\]
3. 计算极限:\(\lim_{x \to 1} \frac{\ln(x) - \ln(1)}{x - 1}\)
解答:利用对数函数的导数性质,得:
\[
\lim_{x \to 1} \frac{\ln(x) - \ln(1)}{x - 1} = \lim_{x \to 1} \frac{1}{x} = 1
\]
微信考研刷题小程序:【考研刷题通】,助你高效备战考研,政治、英语、数学等全部科目刷题练习,随时随地提升解题能力,快来体验吧!【考研刷题通】