Combinatorial Proof
Vandermonde's identity also admits a more combinatorics-flavored double counting proof, as follows. Suppose a committee in the US Senate consists of m Democrats and n Republicans. In how many ways can a subcommittee of r members be formed? The answer is
The answer is also the sum over all possible values of k, of the number of subcommittees consisting of k Democrats and r − k Republicans:
Read more about this topic: Vandermonde's Identity
Famous quotes containing the word proof:
“The chief contribution of Protestantism to human thought is its massive proof that God is a bore.”
—H.L. (Henry Lewis)