a) 123!/121!=121!*122*123/121=122*123
b) 2753!/2752!=2752!*2753/2752!=2753
c) (n+1)!/n!=n!(n+1)/n!=n+1
d) (n+3)!/n!(n+3!)=1/n!
e) (n+1)!*n!/(n-1)!(n+2)!=(n+1)!(n-1)!*n/(n-1)!*(n+1)!(n+2)
Simplificam prin n+1! si se obtine: n(n-1)!/(n-1)!*(n+2). Si acum simplificam prin (n-1)! si se obtine: n/n+2.
