Proof of Convergence/Divergence Unaffected by Series Starting Point

In summary, if an infinite series is convergent from an integer T to infinity, then the series is also convergent from 1 to infinity. Similarly, if a series is convergent from 1 to infinity, then it will also be convergent from T to infinity, regardless of the starting point of the series. This can be proven by considering the definition of a convergent series. However, care must be taken when wording this as there are cases, such as with power series, where this may not hold true.
  • #1
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if we know that an infinite series is convergent from an integer T, to infinity, then the series is convergent from 1 to infinity. conversely, if a series is convergent from 1 to infinity then it is convergent from T to infinity (i.e. starting point of the series does not affect convergence/divergence) This seems obvious but can anyone help me prove it please.
 
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  • #2
This is obvious from the definition of a convergent series. So check the definition again.
 
  • #3
I pulled my lecturer up on this recently, consider the series:

[tex]\sum_{x=10}^{\infty} \frac{1}{(x-7)^2}[/tex]

It converges and if you are interested to:

[tex]\frac{1}{12} \left(2 \pi^2 - 15\right)[/tex]

However:

[tex]\sum_{x=1}^{\infty} \frac{1}{(x-7)^2}[/tex]

Clearly does not converge, so be careful how you word it. Anyway, it's not too difficult to prove, just think of it like:

[tex]a_1 + a_2 + \ldots + a_{t-1} + \sum_{n=t}^{\infty} a_n[/tex]
 
  • #4
Is the series adamg asking about a power series? If so, the answer to his question is yes. However in the more general case as Zurtex showed, it is not true.
 
  • #5
I'd rather say his example

[tex]\sum_{x=1}^{\infty} \frac{1}{(x-7)^2}[/tex]

is not a series, since the 7'th term is not defined.
 

1. What is "Proof of Convergence/Divergence Unaffected by Series Starting Point"?

"Proof of Convergence/Divergence Unaffected by Series Starting Point" is a concept in mathematics that states that the convergence or divergence of a series is not affected by its starting point. This means that if a series converges or diverges, it will do so regardless of where you start summing the series.

2. Why is this concept important?

This concept is important because it allows us to determine the convergence or divergence of a series without having to start from the first term. This can save time and make calculations easier.

3. How is this concept proven?

This concept is proven using mathematical proofs and theorems. One of the most common proofs is the Cauchy's Convergence Test, which states that if the limit of the series approaches zero, then the series converges regardless of the starting point.

4. Can this concept be applied to all series?

Yes, this concept can be applied to all series as long as they meet the criteria for convergence or divergence. However, it is important to note that this concept may not hold true for alternating series or series with other special conditions.

5. How can this concept be used in practical applications?

This concept can be used in various fields of science and engineering, such as in the analysis of data, signal processing, and financial modeling. It allows us to make accurate predictions and calculations without having to start from the beginning of a series.

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