Ответ:
[tex]\frac{x}{A^3_x} = \frac{1}{12} \Rightarrow 12x = A^3_x \Rightarrow \frac{x!}{(x — 3)!} = 12x \Rightarrow x(x — 1)(x — 2) = 12x \Rightarrow x^3 — 3x^2 — 10x = 0 \Rightarrow x(x + 3)(x — 5) = 0 \Rightarrow x = 5[/tex]
[tex]20x = A^2_x\Rightarrow 20x = \frac{x!}{(x — 2)!} \Rightarrow 20x = x(x — 1) \Rightarrow x^2 — 21x = 0 \Rightarrow x(x — 21) = 0 \Rightarrow x = 21[/tex]