Math 2.0

Sequences, series, summability Example

The sequence 1/n tends to zero

Builds on Limit of a sequenceEpsilon-N definition of the limit of a sequence

Example

Let an=1/na_n = 1/n for each integer n≥1n \ge 1. Then an→0a_n \to 0 as n→∞n \to \infty. Let ε>0\varepsilon > 0. By the Archimedean property of ℝ\mathbb{R}, there is a natural number NN with N>1/εN > 1/\varepsilon. For each n≥Nn \ge N we get ∣an−0∣=1/n≤1/N<ε|a_n - 0| = 1/n \le 1/N < \varepsilon. By the epsilon-N definition, this shows 1/n→01/n \to 0.

Remarks

The proof uses the Archimedean property, which says that the natural numbers are not bounded above in ℝ\mathbb{R}. With the algebra of limits, it gives many more limits, for example 1/n2→01/n^2 \to 0 and (n+1)/n→1(n + 1)/n \to 1. Mathlib states it for 1/n1/n over ℝ\mathbb{R} as tendsto_one_div_atTop_nhds_zero_nat.

Reading path

To understand this page from the ground up, read these 5 pages in order. The foundations come first.

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  1. Sequence definition
  2. Real sequence definition
  3. Limit of a sequence definition
  4. Epsilon-N definition of the limit of a sequence statement
  5. The sequence 1/n tends to zero example

Further reading

  1. Web https://en.wikipedia.org/wiki/Limit_of_a_sequence, Examples
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Kindexample
WritingW0 stub
MSC40A05
Instance ofConvergent sequence
UsesLimit of a sequence, Epsilon-N definition of the limit of a sequence

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