# Convergent Sequence with Finite Elements Prepended is Convergent Sequence

Jump to navigation
Jump to search

## Theorem

Let $\struct {R, \norm { \, \cdot \, } }$ be a normed division ring.

Let $\sequence {x_n}$ be a sequence in $R$.

Let $N \in \N$

Let $\sequence {y_n}$ be the sequence defined by:

- $\forall n, y_n = x_{N+n}$

Let $\sequence {y_n}$ be a convergent sequence in $R$ with limit $l$.

Then:

- $\sequence {x_n}$ is a convergent sequence in $R$ with limit $l$.

## Proof

Given $\epsilon \gt 0$

By the definition of a convergent sequence in $R$ with limit $l$ then:

- $\exists N': \forall n \gt N', \norm {y_n - l} \lt \epsilon$

Hence $\forall n \gt \paren {N'+N}$:

\(\displaystyle \norm {x_n - l }\) | \(=\) | \(\displaystyle \norm {y_{n-N } - l }\) | $n \gt N$ | ||||||||||

\(\displaystyle \) | \(\lt\) | \(\displaystyle \epsilon\) | $n-N \gt N'$ |

The result follows.

$\blacksquare$