Let n k m 0 be integers. Consider the following formula: n k ! k m ! D n m ! n m k m !
Chapter 17, Problem 17.17(choose chapter or problem)
Let n k m 0 be integers. Consider the following formula: n k ! k m ! D n m ! n m k m ! : Give two different proofs. One proof should use the factorial formula for n k (Theorem 17.12). The other proof should be combinatorial. Try to develop a question that both sides of the equation answer.
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