Hello I am newbie with Casio Calculators so I need a little help

I am a happy owner of FX-9860gii

I want to solve this equation:

M!

X= ---------------

N! x (M-N)!

I know that can be solved using the Combination function (nCr ) but this is not the idea, the idea is to use X,M and N as variables.

When I try to "write" the equation I receive this answer "syntax error" but I do not know what kind of mistake I did. I wrote the equation in the same way that I wrote here.

If I write this equation, I do not receive the syntax error message so I think the problem is the factorial symbol (!)

M

X= ---------------

N x (M-N)

Thanks in advance.