数学期望E(x)和D(X)怎么求

Question

如题所述

Answer 1

数学期望为
设X是一个随机变量,若E{[X-E(X)]^2}存在,则称E{[X-E(X)]^2}为X的方差,记为D(X),Var(X)或DX.即D(X)=E{[X-E(X)]^2}称为方差,而σ(X)=D(X)^0.5（与X有相同的量纲）称为标准差（或方差）.