#### nomadreid

Gold Member

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(This is not HW, even though it may look a bit like it.)

Using the notation nCr in the combinatorics meaning,

The sum of ((n+k)Cn)*((1/2)^(n+k)) from k = 0 to n equals one. Why?

(I thought it might use the identity (n+1)Cr = nCr+nC(r-1), but that didn't get me anywhere.)

Thanks in advance for any pointers.

Using the notation nCr in the combinatorics meaning,

The sum of ((n+k)Cn)*((1/2)^(n+k)) from k = 0 to n equals one. Why?

(I thought it might use the identity (n+1)Cr = nCr+nC(r-1), but that didn't get me anywhere.)

Thanks in advance for any pointers.

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