Question

Combinări de n luate câte n-2?

Answer 1

$C_{n}^{n-2}=\frac{n!}{(n-2)!(n-n+2)!} =\frac{n!}{2(n-2)!} =\frac{(n-2)!(n-1)n}{2(n-2)!} =\frac{n(n-1)}{2}$

Cam asa