I need to know how to solve this problem, I've been stuck for an hour, please help
Question: find the indicated value of xCx-1 (it's a permutation)

xCy would mean x Choose y and you're asking for xCx or x Choose x.

nCk = C_k^n = {n \choose k} = \frac{n!}{k!(n-k)!}.

so if we do xCx-1 we get:
\frac{x!}{x!(x-x)!} -1 = \frac{x!}{x!0!} -1 = 1-1=0

note: 0!=1 Math Forum - Ask Dr. Math (http://mathforum.org/library/drmath/view/57905.html)

If you think about it, this makes sense because it's like saying, how many ways are there to choose x items from a group of x items. The answer is 1, choose them all.

I hope this helps and is what you were asking about.