Simplifying a symbolic sum

Hi,

I cannot seem to get MathCAD to simplify a symbolic sum. I have tried
several different ways to get it to work and each displays the line in
red and provides a message saying that "No symbolic result was found."
The basic equation that I am feeding MathCAD (Version 8) is:

m
f(x) := sum( ( Y(i,0) * x! ) / ( i! * ( x - i )! )
i=0

where m is defined (m=3) and Y(i,0) is defined in a matrix (in this case
Y(i,0)=[0, 1, 2] transposed), both of which preceed the equation. I have
tried:

f(x) ->
{The sum by itself} ->
f(x) expand,x ->
{The sum by itself} expand,x ->
f(x) simplify ->
{The sum by itself} simplify ->
{The sum substituting permut(x,i) for x!/(x-i)!} simplify ->
{The sum substituting combin(x,i) for x!/(i! * (x-i)!)} simplify ->

but I cannot get this thing to simplify down to x^2, as it should. Yet,
if I put values into f(x), I get the correct numerical results, i.e.

f(8)=64
f(9)=81
f(51)=2601
etc.

Optimizer does not seem to help. Any guidance would be greatly appreciated.

Thanks,
Chuck