# Math Help - Moment generating function for geometric

1. ## Moment generating function for geometric

geometric distribution given by

$Pr(X=x) = (1/a)(1-(1/a)^{x-1})$ where a > 1.

Am I right in saying the distribution above is the same as

$Pr(X=x) = p(1-p)^{x-1}$ which is just the normal geometric pdf or does the change from p to 1/a change something else

2. ## Re: Moment generating function for geometric

Hello,

It doesn't change anything, but I just don't understand where the MGF is in there ?

3. ## Re: Moment generating function for geometric

Originally Posted by whiteboard
geometric distribution given by

$Pr(X=x) = (1/a)(1-(1/a)^{x-1})$ where a > 1.

Am I right in saying the distribution above is the same as

$Pr(X=x) = p(1-p)^{x-1}$ which is just the normal geometric pdf or does the change from p to 1/a change something else
What is raised to the power (x-1) in each of these cases? (and is it a typo?)

CB