- #1

DrummingAtom

- 659

- 2

[tex] \frac{n(n-1)...(n-r+1)}{r!} = \frac {n!}{(n-r)!r!} [/tex]

One of the things I tried was cross multiplied the r! and cancelled it then multilpied the (n-r)!to the other side. Which I was left with:

[tex] [n(n-1)...(n-r+1)]*[(n-r)!]= n! [/tex]

From here I tried expanding the factorials then cancelling stuff but I'm still not seeing the pattern. Thanks for any help.