题目内容
(请给出正确答案)
[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
查看答案
如果结果不匹配,请 联系老师 获取答案
______the ground covered with ice, the road has become very slippery.
A.At
B.Along
C.On
D.With
A、E(ut)=0
B、var(ut)=σ2
C、cov(ut,us)=0
D、cov(xt,ut)=0
E、ut服从分布N(0,σ2)
设二维随机变量(X,Y)的概率密度为
求:
(1)数学期望E(X),E(Y);
(2)方差D(X),D(Y);
(3)协方差cov(X,Y)及相关系数R(X,Y)。
设随机变量X的概率密度为
,(-∞ < x < +∞)
(1)求E(X)及D(X);
(2)求Cov(X,|X|),并问X与|X|是否不相关?
问X与|X|是否相互独立,为什么?
A.E(XY)=E(X)E(Y)
B.X与Y互相独立
C.cov(X,Y)=0
D.D(X+Y)=D(X)+D(Y)
A.X与Y相互独立
B.D(X+Y)=D(X)+D(Y)
C.D(X-Y)=D(X)-D(Y)
D.D(XY)=D(X) D(Y)
He struck the girl in the face and she fell to the ground ___.
A.die
B.death
C.dead
D.deadly