设随机变量 X 服从N（4，2^2） ， Y 服从参数为 3 的泊松分布， X 与 Y 相互独立，则 E(X,Y)= 设X~N(1,2）,Y服从参数为3的泊松分布，且X与Y独立，...
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D(XY)=E[(XY)^2]-[E(XY)]^2
=E(X^2*Y^2)-[E(X)*E(Y)]^2
=E(X^2)*E(Y^2)-(EX)^2*E(Y)^2
=[D(X)+(EX)^2]*[D(Y)+(EY)^2]-(EX)^2*(EY)^2
=(2+1^2)*(3+3^2)-1^2*3^2=27
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1\u3001E(X+Y)=E(X)+E(Y)
2\u3001X\u3001Y\u72ec\u7acb\uff0c\u5219E(XY)=E(X)*E(Y)\uff0cD(X+Y)=D(X)+D(Y)
3\u3001X\u3001Y\u72ec\u7acb\uff0c\u5219f(X)\u3001g(Y)\u4e5f\u72ec\u7acb
4\u3001D(X)=E(X^2)-(EX)^2
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D(x)=3
D(y)=np(1-p)=8*1/3*2/3=8/9,E(y)=8/3
D(X-3Y-4)=
E(X^2)-E^2(X)+E(9Y^2)-E^2(3Y)
=D(x)+D(3Y)=3+8=11
你的问题如果是E（XY）的话，那么根据相互独立就等于=EXEY=4*3=12。不懂的话可以继续问我。
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