Hello, I have recently enrolled in a 3rd year Introductory Probability course.

I'm having a pretty tough time with the course so I came to this forum again to seek some guidance.

When looking at geometric random variables I was asked to find the expected value of r^X, where X is a geometric rv.

I know that E(X) = Sum(n*(1-p)^(n-1)*p) in a geometric series... but it confuses me when I have to find E(r^X).

What do I have to do in this case?