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 Subject: "Prove n choose r" Previous Topic | Next Topic
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Proof Pudding
guest
Feb-13-02, 04:22 PM (EST)

"Prove n choose r"

 Hi all, I have been ask to look at the problem of proving by induction that n C r = (n!)/((n-r)!r!) , 0<= r <=nAnd I dont know where to start?? For the basis do I take n as being 0, if so r must = 0, there for the basis says n C r = 0 C r = 1.But what shall the inductive step consist of? If I take (n+1) C r will this work, because r isnt changing in this step so will it be a propor proof???Please anybody help I am a bit'stuck.Thanks.

alexb
Charter Member
681 posts
Feb-13-02, 04:26 PM (EST)

1. "RE: Prove n choose r"
In response to message #0

 >But what shall the inductive step consist of? Assume you proved the formula for all n less than N and all r not greater than n. In other words, assume you know nCr as long as n < N. Now prove the formula for n = N and all r <= N.

Sumudu
guest
Mar-25-02, 11:05 PM (EST)

2. "RE: Prove n choose r"
In response to message #0

 think of pascal's triangle