Question

Alguém me salva nessa

Answer 1

$\frac{n!}{(n-1)!} = \frac{n*(n-1)(n-2)(n-3)(n-4)...(n-(n-1))}{(n-1)(n-2)(n-3)(n-4)...(n-(n-1)} = n$

Imagine que fosse: 
$\frac{9!}{8!} = \frac{9*(9-1)(9-2)(9-3)(9-4)(9-5)(9-6)(9-7)(9-8)}{8*(8-1)(8-2)(8-3)(8-4)(8-5)(8-6)(8-7)} = 9$