2.
the answer is
[tex](n-r)!=1\cdot2\cdot3\cdot4\cdot\ldots\cdot(n-r-1)\cdot(n-r)[/tex]Explanation
The factorial of a number is the multiplication of all the previous numbers of the number given, for example
[tex]5!=1\cdot2\cdot3\cdot4\cdot5=120[/tex]