The mathematical expectation of the difference of 1, x, y is equal to the difference of their respective mathematical expectations, which is the same as the difference; The same is true of the product sum quotient, but it requires that X and Y are independent of each other, and the difference sum has no requirements for X and Y. ..

They are all equal. Because X and Y are opposite events, they must be independent of each other.

3. Same as above, but pay attention to product sum quotient. When they are established, they are conditional, that is, two or more random variables should be independent of each other.