Help: sum of binomial coefficents

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    Binomial Sum
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Discussion Overview

The discussion revolves around deriving a closed formula for the sum of the first s binomial coefficients, specifically \(\sum_{k=0}^{s} \left({{n}\atop{k}}\right)\) where \(s < n\). Participants are exploring potential methods and existing knowledge related to binomial coefficients in the context of an upcoming exam.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested, Homework-related

Main Points Raised

  • One participant seeks help in deriving a closed formula for the sum of the first s binomial coefficients.
  • Another participant expresses skepticism, stating they do not believe such a formula exists.
  • A different participant recalls having seen a formula in a textbook but cannot remember the details and intends to look it up.
  • One participant mentions that the sum of the binomial coefficients in the n-th row of Pascal's Triangle equals \(2^n\), noting the indexing of the rows.
  • A later reply corrects the previous statement, indicating that the answer \(2^n\) pertains to the case when \(s = n\), not when \(s < n\).
  • Another participant asserts that no formula exists for the case when \(s < n\) and references a book titled "A=B" for methods to simplify binomial summations.
  • This participant also mentions the existence of algorithms that can determine whether a formula exists or not.

Areas of Agreement / Disagreement

Participants express differing views on the existence of a closed formula for the sum of the first s binomial coefficients, with some believing a formula exists and others asserting that it does not. The discussion remains unresolved regarding the derivation of such a formula.

Contextual Notes

There are references to specific resources and methods for simplifying binomial summations, but no consensus on the existence of a closed formula for the case of \(s < n\). The discussion includes varying levels of confidence in the claims made.

thealchemist83
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Help: sum of binomial coefficents !

Hello!
I cannot figure out how to derive a closed formula for the sum of "the first s" binomial coefficients:

[tex]\sum_{k=0}^{s} \left({{n}\atop{k}}\right)[/tex]

with [tex]s<n[/tex]

Could you please help me find out some trick to derive the formula... I've an exam on monday!

Thank you very much!
 
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thealchemist83 said:
Hello!
I cannot figure out how to derive a closed formula for the sum of "the first s" binomial coefficients:

[tex]\sum_{k=0}^{s} \left({{n}\atop{k}}\right)[/tex]

with [tex]s<n[/tex]

Could you please help me find out some trick to derive the formula... I've an exam on monday!

Thank you very much!

I don't believe there is any such formula.
 
well, i think there is one, because as long as i remember i have seen it in a textbook, but it is quite long i think, and i cannot remember how it was right now. I am going to look at it.
 
Last edited:
atqamar said:
I remember that the n-th binomial coefficients can be seen on the n-th line of the Pascal's Triangle. I also remember that the sum of the numbers in the n-th line of the Pascal's Triangle is [tex]2^n[/tex]. NOTE: The first row is the 0-th row, and the next line is the 1-st.

Edit: Here is some additional information: http://en.wikipedia.org/wiki/Binomial_coefficient#Formulas_involving_binomial_coefficients .


Your answer 2n is for s=n, the original question was for s<n.
 
No formula exists in this case. See the book A=B for how to simplify binomial summations. There exists simple algorithms that will yield a formula or will tell you that no formula exists.
 

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