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I need help with this proof of the recurrence relation for binomial coefficients, I don't get how the author got from green to red : r/askmath
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Binomial series: Lecture 12: Product of binomial coefficients when sum of lower suffices is constant - YouTube
![While finding sum of binomial coefficients,why or how can we change index of Σ? - Mathematics Stack Exchange While finding sum of binomial coefficients,why or how can we change index of Σ? - Mathematics Stack Exchange](https://i.stack.imgur.com/cyU36.png)
While finding sum of binomial coefficients,why or how can we change index of Σ? - Mathematics Stack Exchange
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summation - Confusion about proof involving sums and binomial coefficients - Mathematics Stack Exchange
![Alternative definition of binomial coefficients for negative arguments and associated documentation · Issue #14577 · sympy/sympy · GitHub Alternative definition of binomial coefficients for negative arguments and associated documentation · Issue #14577 · sympy/sympy · GitHub](https://user-images.githubusercontent.com/28682735/78073968-72c9d880-73bf-11ea-99ac-3abfb97bfbe3.png)
Alternative definition of binomial coefficients for negative arguments and associated documentation · Issue #14577 · sympy/sympy · GitHub
![Alternative definition of binomial coefficients for negative arguments and associated documentation · Issue #14577 · sympy/sympy · GitHub Alternative definition of binomial coefficients for negative arguments and associated documentation · Issue #14577 · sympy/sympy · GitHub](https://user-images.githubusercontent.com/28682735/78071571-65aaea80-73bb-11ea-8ba5-85da766a3730.png)
Alternative definition of binomial coefficients for negative arguments and associated documentation · Issue #14577 · sympy/sympy · GitHub
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