permutation

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abrar fiaz
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Joined: Sat Feb 13, 2016 10:42 pm

permutation

Unread post by abrar fiaz » Wed Oct 18, 2017 4:48 pm

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here onushiddhanto 2 keno n factorial/n - r factorial ??

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samiul_samin
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Re: permutation

Unread post by samiul_samin » Tue Feb 13, 2018 11:30 pm

It is just an easy algebric manipulation. because $(n-r)!=n*(n-1)*(n-2)*...2*1$ so the numerator will be$n!$. And we are done.☺☺☺
$\int^{\infty}_0 e^{-x} dx=1$

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