So I can not figure out the combinatorial proof for Vandermonde's Identity for the example $\sum_{i=0}^k \binom {k} {i}^2 = \binom {2k} {k}$ Any help would be appreciated.

Figured it out, thanks :)


marked as duplicate by Elaqqad, Brian M. Scott combinatorics Apr 8 '15 at 21:27

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  • $\begingroup$ There’s one in the Wikipedia article. $\endgroup$ – Brian M. Scott Apr 8 '15 at 21:19
  • $\begingroup$ I'm sorry the post I selected is not the right one, I did not see the "inductive proof", maybe this one provides a combinatorial proof $\endgroup$ – Elaqqad Apr 8 '15 at 21:26
  • $\begingroup$ @Haris: The excellent answer to this question may also be useful. $\endgroup$ – Brian M. Scott Apr 8 '15 at 21:28