n(n-1)!/(n+2)!= n(n-1)!/(n-1)!n(h+1)(n+2)=1/(n-1)(n+2)

(n+1)!(n-1)/n(n+2)! = ( 1*2*3*...*(n+1)(n-1) ) / ( n*(1*2*3...*(n+1)(n+2)) ) = (n-1)/(n(n+2))