The problem is to evaluate the infinite sum $\sum_{k=1}^{\infty} (\frac{1}{k} - \frac{1}{k+1})$.

AnalysisInfinite SeriesTelescoping SeriesLimitsSummation
2025/3/7

1. Problem Description

The problem is to evaluate the infinite sum k=1(1k1k+1)\sum_{k=1}^{\infty} (\frac{1}{k} - \frac{1}{k+1}).

2. Solution Steps

This is a telescoping series. Let SnS_n be the nn-th partial sum of the series.
Sn=k=1n(1k1k+1)S_n = \sum_{k=1}^{n} \left( \frac{1}{k} - \frac{1}{k+1} \right)
Sn=(1112)+(1213)+(1314)++(1n1n+1)S_n = \left( \frac{1}{1} - \frac{1}{2} \right) + \left( \frac{1}{2} - \frac{1}{3} \right) + \left( \frac{1}{3} - \frac{1}{4} \right) + \cdots + \left( \frac{1}{n} - \frac{1}{n+1} \right)
The intermediate terms cancel out, so we are left with:
Sn=11n+1S_n = 1 - \frac{1}{n+1}
The infinite sum is the limit of the partial sums as nn approaches infinity:
k=1(1k1k+1)=limnSn=limn(11n+1)\sum_{k=1}^{\infty} \left( \frac{1}{k} - \frac{1}{k+1} \right) = \lim_{n \to \infty} S_n = \lim_{n \to \infty} \left( 1 - \frac{1}{n+1} \right)
Since limn1n+1=0\lim_{n \to \infty} \frac{1}{n+1} = 0, we have:
limn(11n+1)=10=1\lim_{n \to \infty} \left( 1 - \frac{1}{n+1} \right) = 1 - 0 = 1

3. Final Answer

1

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