[tex] C(n,r) = \frac{n!}{r!(n - r)!} [/tex]
[tex] C(n,n) = \frac{n!}{n!(n - n)!} [/tex]
[tex] C(n,n) = \frac{n!}{n!0!} [/tex]
[tex] C(n,n) = \frac{n!}{n! \times 1} [/tex]
[tex] C(n,n) = \frac{n!}{n!} [/tex]
[tex] C(n,n) = 1 [/tex]
