题目内容
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[主观题]
______the ground covered with ice, the road has become very slippery.A.AtB.AlongC.OnD.With
______the ground covered with ice, the road has become very slippery.
A.At
B.Along
C.On
D.With
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______the ground covered with ice, the road has become very slippery.
A.At
B.Along
C.On
D.With
Y)=___________.
对随机变量X和Y,已知D(X)=2,D(Y)=3,cov(X,Y)=-1,计算cov(3X-2Y+1,X+4Y-3).
设随机变量(X1,X2)具有概率密度。
求E(X1),E(X2),COV(X1,X2),D(X1+X2)。
设随机向量(X,Y)的联合分布律为求E(X) ,E(Y),E(X-2Y) ,E(3XY),D(X),D(Y),cov(X,Y),ρX.Y.
设X,Y为随机变量,E(X)=E(Y)=1,Cov(X,Y)=2,则E(2XY)=
A -6
B -2
C 2
D 6