Question

Quanto fica:
x! / (x -1)! + (x-1)! / (x-2)! = 19

Answer 1

lembrando que:

$n!=n.(n-1)!$

cálculo:

$\frac{x!}{(x-1)!} + \frac{(x-1)!}{(x-2)!} =19\\ \\ \frac{x(x-1)!}{(x-1)!} + \frac{(x-1)(x-2!)}{(x-2)!)} =19\\ \\x+x-1=19\\ \\2x=20\\ \\\boxed{\therefore~x=10}$