Question

设随机变量的概率密度函数为f(x)=k/(1+x^2),-1

Answer 1

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