«Banaketa binomial»: berrikuspenen arteko aldeak

 
::<math>\begin{array}{rcl}
var[Y] & = & var[X_1]+var[X_2]+\ldots+var[X_n]\\
& = & pq+pq+\ldots+pq\\
& = & npq\\
 
::<math>\begin{array}{rcl}
E[X(X-1)] & = & \sum_{i=0}^nx(x-1)p(x)\\
& = & \sum_{x=0}^nx(x-1)\frac{n!}{x!(n-x)!}p^x(1-p)^{n-x}\\
& = & \sum_{x=0}^nx(x-1)\frac{n!}{(x-2)!(n-x)!}p^x(1-p)^{n-x}\\
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