问题描述: 若xy独立 证明的D(xy)=D(X)D(Y)+(E(x))^2D(Y)+E((Y))^2D(x) 1个回答 分类:数学 2014-10-16 问题解答: 我来补答 DX=EX^2-(EX)^2DY=EY^2-(EY)^2EXY=EXEYDXY=E(XY)^2-(EXY)^2=(EX^2)(EY^2)-(EXY)(EXY)=DXDY+EX^2(EY)^2+(EX)^2EY^2-2(EX)^2(EY)^2=DXDY+(EX)^2(EY^2-(EY)^2)+(EY)^2(EX^2-(EX)^2)=D(X)D(Y)+(E(x))^2D(Y)+E((Y))^2D(x) 再问: 谢谢了啊 展开全文阅读