Summation with Binomial Expansion

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SUMMARY

The discussion focuses on proving the relationship involving binomial coefficients: \(\sum_{i=0}^k \text{Binomial}[n+1,k-2i] - \sum_{i=0}^k \text{Binomial}[n,k-2i]=\sum_{i=0}^k \text{Binomial}[n,k-1-2i]\). Participants highlighted the need for accurate application of binomial definitions, specifically correcting the formula to \(\begin{pmatrix}n\\k\end{pmatrix}=\frac{n!}{k!(n-k)!}\). Concerns were raised regarding the validity of the summation when \(k-2i<0\), indicating that the terms would evaluate to zero in such cases.

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Jake1802
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Homework Statement


How can i prove this relationship
\sum _{i=0}^k \text{Binomial}[n+1,k-2i] - \sum _{i=0}^k \text{Binomial}[n,k-2i]=\sum _{i=0}^k \text{Binomial}[n,k-1-2i]

Homework Equations


Binomial (n,k)=n^k/k!

The Attempt at a Solution



I attempted subbing into mathyematica but this didn't work so i attempted by hand and got completely lost. Any helpful comments would be helpful.
Result from Mathematica
-Binomial[n, -1 + k] HypergeometricPFQ[{1, 1/2 - k/2,
1 - k/2}, {1 - k/2 + n/2, 3/2 - k/2 + n/2}, 1] -
Binomial[n,
k] HypergeometricPFQ[{1, 1/2 - k/2, -(k/2)}, {1/2 - k/2 + n/2,
1 - k/2 + n/2}, 1] +
Binomial[1 + n,
k] HypergeometricPFQ[{1, 1/2 - k/2, -(k/2)}, {1 - k/2 + n/2,
3/2 - k/2 + n/2}, 1]
 
Last edited:
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Fixed your LaTex. Is this the relation you're supposed to prove?

[tex]\sum_{i=0}^k \begin{pmatrix}n+1\\k-2i\end{pmatrix} - \sum_{i=0}^k \begin{pmatrix}n\\k-2i\end{pmatrix}=\sum_{i=0}^k \begin{pmatrix}n\\k-1-2i\end{pmatrix}[/tex]

I don't think it's correct because k-2i<0 for some values of i in the summation.

Binomial (n,k)=n^k/k!
That's not right. It should be

[tex]\begin{pmatrix}n\\k\end{pmatrix}=\frac{n!}{k!(n-k)!}[/tex]
 
but when k-2i<0 the value will be zero
 

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