X服从泊松分布求E[X(X-1)]

来源:学生作业帮助网 编辑:六六作业网 时间:2024/05/24 04:54:09
X服从泊松分布求E[X(X-1)]X服从泊松分布求E[X(X-1)]X服从泊松分布求E[X(X-1)]设X服从泊松分布,参数为λ,那么EX=λ,DX=λ,所以E[X(X-1)]=E(X^2)-EX=D

X服从泊松分布求E[X(X-1)]
X服从泊松分布求E[X(X-1)]

X服从泊松分布求E[X(X-1)]
设X服从泊松分布,参数为λ,那么
EX=λ,DX=λ,
所以 E[X(X-1)]
=E(X^2)-EX
=DX+(EX)^2-EX
=λ+λ^2-λ
=λ^2.
也可以直接根据定义
E[X(X-1)]
=sum(n(n-1)*λ^n/n!*e^(-λ)),n=0..∞
=sum(λ^2*λ^(n-2)/(n-2)!*e^(-λ)),n=2..∞
=λ^2*sum(λ^n/n!*e^(-λ)),n=0..∞
=λ^2*1
=λ^2