Hei! :)
4×A⁵ₓ₊₁=9×Aₓ⁵
[tex]4*\frac{(x+1)!}{(x-4)!} =9*\frac{x!}{(x-5)!} \\= > 4*(x-3)(x-2)(x-1)x(x+1)=9*(x-4)(x-3)(x-2)(x-1)x\\= > 4*(x-3)(x-2)(x-1)x(x+1)-9*(x-4)(x-3)(x-2)(x-1)x=0\\= > x(x-3)(x-2)(x-1)(4(x+1)-9(x-4))=0\\= > x(x-3)(x-2)(x-1)(4x+4-9x+36)=0\\= > x(x-3)(x-2)(x-1)(-5x+40)=0[/tex]
Solutiile lui x sunt {0, 3, 2, 1 si 8}
=> Varianta corecta este b).