If you have:

n!(n+1), that simplifies to (n+1)!

but how would you do that for:

(n-r)!(n-r-1)!

or

(r+1)!(r!)

Thanks in advance.

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- Jun 4th 2009, 12:57 PMGulhelp with simplifying something
If you have:

n!(n+1), that simplifies to (n+1)!

but how would you do that for:

(n-r)!(n-r-1)!

or

(r+1)!(r!)

Thanks in advance. - Jun 4th 2009, 01:07 PMPlato
$\displaystyle \begin{gathered}

\left( {n - r} \right)!\left( {n - r - 1} \right)! = \left( {n - r} \right)\left[ {\left( {n - r - 1} \right)!} \right]^2 \hfill \\

\left( {r + 1} \right)!\left( {r!} \right) = \left( {r + 1} \right)\left( {r!} \right)^2 \hfill \\

\end{gathered} $