Срочно нужна помощь другу

[latex] \frac{x}{A_x^3} = \frac{1}{12} , \\ \frac{x}{\frac{x!}{(x-3)!}} = \frac{1}{12} , \\ \frac{x}{(x-2)(x-1)x} = \frac{1}{12} , \\ \frac{1}{(x-2)(x-1)} - \frac{1}{12} = 0, \\ \frac{12-(x-2)(x-1)}{12(x-2)(x-1)} = 0, \\ -12+x^2-3x+2=0, \\ x^2-3x-10=0, \\ x_1=-2\ \textless \ 0, x_2=5, \\ x=5.[/latex]