1, the expectation of a constant is the constant itself, written as e (c) = c

2. A constant multiplied by the expectation of the random variable X is equal to this constant multiplied by the expectation of X, and it is written that E(cX)=cE(X)E(cX)=cE(X).

3. The expectation of the random variable X plus Y is equal to the sum of the respective expectations of X and Y. Write E (X+Y) = E (X)+E (Y) E (X+Y) = E (X)+E (Y).

4. The expectation of the random variable X minus Y is equal to the difference between the respective expectations of X and Y, and E(X? Y)=E(X)？ E(Y)E(X？ Y)=E(X)？ Italian (Italian) people

Application of expected value:

In statistics, when estimating the expected value of a variable, the common method is to measure the value of this variable repeatedly, and then estimate the expected value of this variable with the average value of the obtained data.

In probability distribution, expected value and variance or standard deviation are important characteristics of distribution.

In classical mechanics, the algorithm of the center of gravity of an object is very similar to the algorithm of expected value.