设随机变量(X,Y)的联合概率密度分别如下答:随机变量(x,y)的联合概率密度分别如下:f(x,y)={ke^-(3x+4y)} ,x,y>0 0 其他 (1)∫∫ f(x,y)dxdy=1 所以∫(0,∞)∫(0,∞)k*e^-(3x+4y)dxdy =k*∫(0,∞)dx ∫(0,∞)e^-(3x+4y)dy =k*∫(0,∞)dx (-1/4)*e^(-3x-4y)(0,∞)=k/4*∫(0,∞)e^(...
设二维随机变量(X,Y)的联合概率密度为f(x,y)=1,0答:^^设随机变量(X,Y)具有概率密度f(x,y)=1/8(x+y),0<x,y<2,求E(X),cov(X,Y),ρXY f(x)=1/4*(x+1),0<x<2 f(y)=1/4*(y+1),0<y<2 EX=∫zhixf(x)dx=7/6 EY=∫yf(y)dy=7/6 EX^dao2=∫x^2f(x)dx=5/3 EY^2=∫y^2f(y)dy=5/3 DX=EX^2-(EX)^2...