设连续型随机变量X的概率密度函数为为f(x)=1/2*e^(-|x|),-∞<x<+∞,求DX EX

Question

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Answer 1

E(x)=∫(-∞,+∞)xf(x)dx=0
D(x)=E(x^2)-(E(x))^2=E(x^2)=∫(-∞,+∞)x^2f(x)dx=2∫(0,+∞)x^2f(x)dx
=∫(0,+∞)x^2e^(-x)dx=-x^2e^(-x)︱(0,+∞)-2∫(0,+∞)xe^(-x)dx=2∫(0,+∞)e^(-x)dx
=2本回答被提问者和网友采纳

Answer 2

放松放松分萨法萨法打算哦