Negative Binomial

[jacky]

Can anyone please confirm if these formulas are correct for negative binomial, thanks.

pdf = [ (x+r-1) nCr (x) ](p^r) (q^x)
cdf = ∑ pdf
E(x) = r*q/p
var(x) = r*q/(p^2)
mgf = [p/(1-q*e^t)]^(x+1)

[NoMoreExams]

A good place to check wikipedia or mathworld.wolfram.com

[jacky]

I checked and they give me 2 different answer.
Thats why I want to verify if this is correct, thanks

[NoMoreExams]

Well wikipedia disagrees with you right?

Now in the mathworld link, it might look different but write out (x+r-1) C (r-1) and compare that to (x+r-1) C (x). You should be able to prove they are the same.