Discrete random variables X satisfies \ (P (X = I) = P_i \) , we define \ (f (x) = \ sum_ {i} p_ix ^ it \) of \ (X \) is the probability generating function.
nature:
f(1)=1
X is desirably \ (f '(1) \ )
As for the variance you can own push,
Binomial distribution \ (B ~ (n, p ) \) of \ (f (x) = ( px + 1-p) ^ n \)
It represents a random variable by multiplying the sum of two random variables
There are also nested operations, it seems to be the representative of multiplying? Specifically remember. Elderly retired players decadent cause brain memory loss.