Resposta:

n = 3

Explicação passo a passo:

[tex]A_n_,_3=3(n-1)\\\\\frac{n!}{(n-3)!} =3(n-1)\\\\\frac{n(n-1)(n-2)(n-3)!}{(n-3)!}=3(n-1)\\\\n(n-1)(n-2)=3(n-1)\\\\n(n-2)=3\\\\n^2-2n=3\\\\n^2-2n+1=3+1\\\\(n-1)^2=4\\\\n-1=2\\\\n=3\\ou\\n-1=-2 \\\\n=-1~(n\tilde ao~serve)[/tex]