Thread: 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!!

Just to aid in reading...

Prove that .


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

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