2)
A³x=56x
x!/(x-3)!=56x
(x-3)!*(x-2)*(x-1)*x/(x-3)!=(x-2)*(x-1)*x=(x²-3x+2)*x=56x
(x²-3x+2)x=56x |÷x
x²-3x+2=56
x²-3x-54=0 D=225 √D=15
x₁=9 x₂=-6 ∉
Ответ: x=9.
3)
A²(x-1)=30
(x-1)!/(x-1-2)!=30
(x-1)!/(x-3)!=30
(x-3)!*(x-2)*(x-1)/(x-3)!=30
(x-2)*(x-1)=30
x²-3x+2=30
x²-3x-28=0 D=121 √D=11
x₁=7 x₂=-4 ∉
Ответ: x=7.
5)
C ²(x-5)=21
(x-5)!/((x-5-2)!*2!)=21
(x-5!/((x-7)!*2)=21
(x-7)!*(x-6)*(x-5)/((x-7)!*2)=21
(x-6)*(x-5)/2=21
x²-11x+30=42
x²-11x-12=0 D=169 √D=13
x₁=12 x₂=-1 ∉
Ответ: x=12.