设D(X)=1, D(Y)=4, cov(X,Y)=0.5,则D(X+Y)= ( ).
A: 3
B: 5
C: 4
D: 6
A: 3
B: 5
C: 4
D: 6
举一反三
- 设X,Y为随机变量,且D(X+Y)=7,D(X)=4,D(Y)=1,则Cov(X,Y)=
- 设随机变量X,Y有D(X)= 9,D(Y)= 4,ρXY =1/3,则Cov(X,Y)=____
- 设(X, Y)为二维随机变量，已知Var(X)=3, Var(Y)=6, Cov(X,Y)=2，则Cov(X+Y, Y) = A: 8 B: 9 C: 10 D: 6
- 设D(X)=4,D(Y)=9,03c1(X,Y)=0.5,则D(X-Y)=,D(X+Y)=
- 已知：EX=3，EY＝３。DX＝１，DY＝９。cov(X,Y)=2. 求： 1) E(X+Y)=____________ 2) D(X+Y)=____________ 3) D(X-Y)=____________ 4) cov(2X,Y)=____________ 5) cov(X,3Y)=____________