Resposta:
[tex]\boxed{x=3}[/tex]
Explicação passo-a-passo:
[tex]\boxed{P_x^{2}=C_{x,x-1}}\ \therefore\ \dfrac{x!}{2!}=\dfrac{x!}{(x-1)!(x-(x-1))!}\ \therefore[/tex]
[tex]\dfrac{1}{2!}=\dfrac{1}{(x-1)!}\ \therefore\ (x-1)!=2!\ \therefore\ x-1=2\ \therefore\ \boxed{x=3}[/tex]
