Question

помогите
формула А из n по k=n(n-1)×...×(n-(k-1))​

Answer 1

$A_{x-3} ^{2} =2x-3\\ \\ A_{x-3} ^{2} =\frac{(x-3)!}{(x-3-2)!} =\frac{(x-3)(x-3-1)(x-3-2)!}{(x-3-2)!} =\\ \\ (x-3)(x-3-1)=(x-3)(x-4)=2(x-3)\\ \\ (x-3)(x-4)-2(x-3)=0\\ (x-3)(x-4-2)=0\\ (x-3)(x-6)=0\\ \\ x-3 =0\\ ili\\ x-6=0\\ \\ Otvet:\\\\ x=3\\ ne\\ podxodit\\ x-3\geq 2\\ x\geq 5\\\\ Otbet: x= 6$