Let X be a geometric random variable with parameter $p$ compute $E[X^3]$.
How would I approach this and how would I simplify the series? Can I use a moment generating function?
I am able to write out a formula for expectation, I believe it is the sum from 1 to n of $k^3p(1-p)^{k-1}$, I apologize for the terrible notation but I am not sure how to proceed from here.