Because (x, y) is a two-dimensional discrete random variable.

So xy is also a discrete random variable.

Find the probability distribution list of xy first.

Find the expectation of xy again: for example, p (x = 0) = 1/2, p (x =1) =1/2, p (y =1)

When all available values of a random variable are a discrete set, it is called a discrete random variable, otherwise it is called a non-discrete random variable, which is a very large class, and one of them is extremely common. The value of a random variable is an (n)-dimensional continuous space.

Calculation method:

A random variable is a finite or countable variable within a certain interval. For example, the number of births and deaths in a certain area in a certain year, the effective number and ineffective number of a certain drug in treating a certain patient, etc. Discrete random variables are usually classified according to probability quality function, which are mainly divided into Bernoulli random variables, binomial random variables, geometric random variables and Poisson random variables.