排列數

將組合作排序就是排列

$\small\left( \begin{array}{} 3 \\ 2 \end{array} \right)$×2!

$\small\left( \begin{array}{} n \\ m \end{array} \right)$ × m! = $\large\frac{n!}{m!(n-m)!}$× m!= $\large\frac{n!}{(n-m)!}$

$P_m^n$=$\large\frac{n!}{(n-m)!}$

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