二维离散型随机变量方差怎样算
x/y 12
10.10.3
20.40.2 求D(X) D(Y) 标准协方差.谢谢
人气：145 ℃ 时间：2020-03-28 18:31:53
解答
E(X) = ∑ xP(x,y) = 1*0.1 + 1*0.3 + 2*0.4 + 2*0.2 = 1.6D(X) = E[(X-EX)^2] = ∑ (x-EX)^2 P(x,y) = (1-1.6)^2*0.1+(1-1.6)^2*0.3+(2-1.6)^2*0.4+(2-1.6)^2*0.2= 0.6^2*0.4 + 0.4^2*0.6 = 0.24E(Y) = ∑ yP(x,y) ...
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