SOLUTION: Prove that nCr=nCn-r

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Question 1121719: Prove that nCr=nCn-r
Answer by rothauserc(4718) About Me  (Show Source):
You can put this solution on YOUR website!
nCr = n! / (r! * (n-r)!)
:
nCn-r = n! / ((n-r)! * (n-(n-r))!) =
:
n! / ((n-r)! * (n-n+r)!) =
:
n! / ((n-r)! * r!) =
:
Note multiplication is commutative(a * b = b* a), therefore
:
n! / (r! * (n-r)!)
:
QED
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