= E(X²)E(Y²)-2E²(X)E²(Y)+E²(X)E²(Y)= E(X²)E(Y²)-E²(X)E²(Y) (2)如果E(X) = E(Y) = 0,那么D(XY) = E(X²)E(Y²) = D(X)D(Y), (3)也就是说当 X,Y独立,且X,Y的数学期望均为零时,X,Y乘积 XY的方差D(XY)等于:D(XY) = D(X...
解析 D(XY) = E{[XY-E(XY)]^2} (1) = E{X²Y²-2XYE(XY)+E²(XY)} = E(X²)E(Y²)-2E²(X)E²(Y)+E²(X)E²(Y) = E(X²)E(Y²)-E... 分析总结。 dxyexyexy21ex²y²2xyexye²xyex²ey²2e²xe²ye²xe²yex²ey²e反馈...
D(XY) = E{[XY-E(XY)]^2} = E{X²Y²-2XYE(XY)+E²(XY)} = E(X²)E(Y²)-2E²(X)E²(Y)+E²(X)E²(Y) = E(X²)E(Y²)-E²(X)E²(Y) 如果E(X) = E(Y) = 0, 那么D(XY) = E(X²)E(Y²) = D(X)D(Y), 也就是说当 X,Y独立,且...
D(XY) = E{[XY-E(XY)]^2} = E{X²Y²-2XYE(XY)+E²(XY)} = E(X²)E(Y²)-2E²(X)E²(Y)+E²(X)E²(Y)= E(X²)E(Y²)-E²(X)E²(Y)如果 E(X) = E(Y) = 0,那么 D(XY) = E(...
如果 E(X) = E(Y) = 0,那么 D(XY) = E(X²)E(Y²) = D(X)D(Y)， 也就是说当X，Y独立，且X,Y的数学期望均为零时，X,Y乘积 XY的方差D(XY)等于：D(XY) = D(X)D(Y)表示方法 随机试验结果的量的表示。例如掷一颗骰子出现的点数，电话交换台在一定时间内收到...
百度试题 结果1 题目X、Y为两个独立的随机变量,其各自的期望,方差均已知,D(XY)=? 相关知识点: 排列组合与概率统计 统计与统计案例 极差、方差与标准差 方差 试题来源: 解析 D(XY)=E(X2×Y2)-[E(X2=E(X2)E(Y2)-[E(X)E()]2 反馈 收藏 ...
D(xy)=E(x²y²)-E²(xy)=E(x²)E(y²)-E²(x)E²(y) D(x)=E(x²)-E²(x) D(y)=E(y²)-E²(y) E²(x)>=0 E(x²)>=0 所以 D(x)D(y)=E(x²)E(y²)-E²(x)E²(y)-E²(x)E(y²)-E(x²)E²(y) =D(xy)-E²(x)E(...
当X、Y相互独立,且 E(X) = E(Y) = 0 时,D(XY) = E{[XY-E(XY)]²} = E{[XY-E(X)E(Y)]²} = E{X²Y²} = E(X²) E(Y²) = [E(X²)-E²(X)] [E(Y²)-E²(Y)] = D(X)D(Y)00分享举报为...
【答案】：证 积的方差．在例3.20题1中已经证明：此时X2与Y2相互独立．于是，有D(XY)=E[XY-E(XY)]2=E(X2Y2)-[E(XY)]2=E(X2)E(Y2)-[E(X)E(Y)]2=[D(X)+(E(X))2][D(Y)+(E(Y))2]一[E(X)E(Y)]2=D(X)D(Y)+[E(Y)]2D(X)+[...
若X与Y相互独立，D(X±Y)=DX+DY