Răspuns :
n! supra (n+1)!(n-1)!(n+2)! din care eliminam n-1 si n+1 si ramane n! supra (n+2)!
[tex] \dfrac{(n+1)!n!}{(n-1)!(n+2)!}= \\ \\ = \dfrac{(n+1)!(n-1)!n}{(n-1)!(n+1)!(n+2)} = \\ \\ = \dfrac{n}{n+2}[/tex]