设随机变量的概率密度函数为f(x)=k/(1+x^2),-1
人气：347 ℃ 时间：2019-11-04 08:36:28
解答
1.∫k/(1+x^2)dx=1-->k=2/π
2.E(x)=(2/π).∫x/(1+x^2)dx=0
3.D(x)=)=(2/π).∫x^2/(1+x^2)dx=4/π-1
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