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 $\displaystyle \displaystyle r{{r-1}\choose{k}} = (r - k){r\choose{k}}$.
Surely you can prove this by evaluating the combinations using the formula
$\displaystyle \displaystyle {n\choose{k}} = \frac{n!}{k!(n-k)!}$...