设 (X+Y)=D(X)+D(Y), 则以下结论正确的是 ()-|||-(A)X,Y不相关 (B)X,Y独立 (C) (rho )_(xy)=1 (D) _(xy)=-1

03)X与Y不相关,即 (rho )_(xy)=0 ,则与之等价-|||-的条件是 () 。-|||-A (X+Y)=D(X-Y)-|||-B D(X-Y)=D

设X,Y为随机变量，且E(XY)=E(X)E(Y),则有( )。A.D(XY)=D(X)D(Y) B.D(X+Y)=D(X)+D(Y)C.X,Y相互

设随机变量X与Y，则下列结论必然正确的有（）A E(X+Y)=E(X)+E(Y)B D(X+Y)=D(X)+D(Y)C 当E(XY)=E(X)E(Y)时，X与Y

如果随机变量X和Y满足D(X+Y)=D(X-Y),则下列各结论正确的是_____A D(Y) =0 B D(X)D(Y) =0 C X和Y相互独立D X和Y不相

21.设 D(X)=25 ,D(Y)=36 ,(rho )_(xy)=dfrac (1)(6) ,求:(1) D(X+Y) ;(2) D(X-Y) .

如果X,Y相互独立,则( ).(A)D(XY)= D(X)D(Y)(B)D(XY)= D(X)D(Y)(C)D(XY)= D(X)D(Y)(D)D(XY)=

已知D(X)=4，D(Y)=1，rho xy=0.6，求D(X+Y)，D(3X-2Y)已知D(X)=4，D(Y)=1，，求D(X+Y)，D(3X-2Y)

对两个随机变量X与Y，若 E(XY)=E(X)E(Y)，则A D(X+Y)=D(X)+D(Y)B X 与 Y 相互独立C X 与 Y 不相互独立D D(XY)=

设X和Y为两个随机变量，已知E(XY)=E(X)E(Y)，则必有（）A D(XY)=D(X)·D(Y)B D(X+Y)=D(X)+D(Y)C X和Y相互独立D

3、设X与Y的期望与方差都存在,且-|||-(X+Y)=D(X)+D(Y), 则以下不正确的是-|||-X与Y不相关;-|||-X与Y不一定独立;-|||-E(