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\(\lim _{n \rightarrow \infty}\left\{\frac{1}{n+m}+\frac{1}{n+2 m}+\frac{1}{n+3 m}+\ldots+\frac{1}{n+n m}\right\}=\)
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Verified Answer
The correct answer is:
\(\frac{\log _e(1+m)}{m}\)
Given,
\(\begin{aligned}
& =\lim _{n \rightarrow \infty} \frac{1}{n}\left(\sum_{k=1}^n \frac{1}{1+m\left(\frac{k}{n}\right)}\right) \\
& =\int_0^1 \frac{1}{1+m x} d x=\frac{1}{m} \int_0^1 \frac{m}{1+m x} d x \\
& =\frac{1}{m}\left[\log _e(1+m x)\right]_0^1=\frac{1}{m}\left[\log _e(1+m)-\log (1)\right] \\
& =\frac{\log _e(1+m)}{m}
\end{aligned}\)
\(\begin{aligned}
& =\lim _{n \rightarrow \infty} \frac{1}{n}\left(\sum_{k=1}^n \frac{1}{1+m\left(\frac{k}{n}\right)}\right) \\
& =\int_0^1 \frac{1}{1+m x} d x=\frac{1}{m} \int_0^1 \frac{m}{1+m x} d x \\
& =\frac{1}{m}\left[\log _e(1+m x)\right]_0^1=\frac{1}{m}\left[\log _e(1+m)-\log (1)\right] \\
& =\frac{\log _e(1+m)}{m}
\end{aligned}\)
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