# I don't know how this happen!!! Help me in fatorial?

##
I would like to understand how this happens...

#i!((n),(i)) = n(n-1)...(n-i+1)#

I know that #i!((n),(i)) = i! frac{n!}{i!(n-i)!}# , but I don't know how to get this equality above.

I would like to understand how this happens...

I know that

##### 1 Answer

Cancelling the relevant factorials gives us the equality. See below.

#### Explanation:

Let's look at

The

Furthermore, recall that

Well, somewhere before

Then,

So, we're left with

because since