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Math Help - Proof help

  1. #1
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    Proof help

    Prove that r[(r-1)Ck] = rCk(r-k)

    This may be hard to read... Prove that r times (r-1) choose k = r choose k time (r-k)

    I don't have a clue how to show this. Any help is greatly appreciated!!
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  2. #2
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    Just to aid in reading...

    Prove that \displaystyle r{{r-1}\choose{k}} = (r - k){r\choose{k}}.


    Surely you can prove this by evaluating the combinations using the formula

    \displaystyle {n\choose{k}} = \frac{n!}{k!(n-k)!}...
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