离散型随机变量的数学期望具有线性性:对任意常数ci,i=1,2,…,n及b,有E(∑ni=1ciζi+b)=∑ni=1ciEζi+b.特别地,若ζ=ζ1+ζ2+…+ζn,则Eζ=E(ζ1+ζ2+…+ζn)=Eζ1+Eζ2+…+Eζn.由以上性质可以知道,随机变量的和的期望等于随机变量的期望的和.因此,要求一个比较复杂的随机变 The mathematical expectation of a discrete random variable has linearity: for any constant ci, i=1, 2,..., n and b, there is E(∑ni=1ciζi+b)=∑ni=1ciEζi+b. In particular, if ζ=ζ1+ζ2+...+ζn, then Eζ=E(ζ1+ζ2+...+ζn)=Eζ1+Eζ2+...+Eζn. It can be known from the above properties that the expectation of the sum of random variables is equal to the expected sum of random variables. Requires a more complex random variation