permutation

why is nPk "n!/(n-k)!" ?
i'm understanding that nPk = n*(n - 1)***(n - k + 1).
uhh...

Quote:

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Originally Posted by miki

why is nPk "n!/(n-k)!" ?
i'm understanding that nPk = n*(n - 1)***(n - k + 1).
uhh...

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$\displaystyle N!=N\cdot(n-1)\cdots(N-k+1)(N-k)!$

Example $\displaystyle _{10}P_4=10\cdot 9\cdot 8\cdot 7=\frac{10!}{(10-4)!}$

thanks a lot !
i understod your reply meaning.
i try it!