X 7.1 . 1 ) 2x 3.x 15 20 + 12 : 3 ) m n1 + а - 1 1 - а 7.2 . 1 ) 3х y 12.x 3 4a 4a 8a 2 ) + 25 35 21 Заb 10x'y 2 ) 4xy 21a b 12ab : 8a . 250 15.x 3 ) 5x : y 7.3 . 1 ) ( m + n ) ( m - n ) ; 2 ) ( x + 5 ) ( x - 5 ) ; 3 ) ( a - 3 ) ( 3 + a ) ; 4 ) ( y + 2 ) ( 2 - y ) . 7.4.1 ) ( x + 2 ) : 2 ) ( 3x - y ) " ; 3 ) ( 5a + b ) ; 7.5 . 1 ) ( x + 1 ) * ( x2 - x + 1 ) ; 2 ) ( a - 2 ) ( a + 2a + 4 ) ; 4 ) ( a + b ^ ) . m m - 2n :) 3 ) + mn + 4n " ) . 2 4 :​

Объяснение:

1.

C⁵ₓ₊₁=(3/8)*A³ₓ

(x+1)!/((x+1-5)!*5!)=(3/8)*x!/(x-3)!

(x+1)!/((x-4)!*5!)=(3/8)*x!/((x-4)!(x-3))

x!*(x+1)/5!=(3/8)*x!/(x-3)

(x+1)/5!=(3/8)/(x-3)

(x-3)*(x+1)=(3/8)*120

x²-2x-3=45

x₂-2x-48=0     D=196    √D=14

x₁=-6 ∉      x₂=8.

ответ: х=8.

2.

Cˣ⁻⁴ₓ₊₁=(7/15)*A³ₓ₊₁

(x+1)!/((x+1-(x-4))!*(x-4)!=(7/15)*(x+1)!/(x+1-3)!

(x+1)!/(5!*(x-4)!=(7/15)*(x+1)!/(x-2)!

1/(5!*(x-4)!)=(7/15)/((x-4)!*(x-3)*(x-2))

1/5!=(7/15)/((x-3)*(x-2))

15*(x-3)*(x-2)=7*5!

15*(x²-5x+6)=7*120  |÷15

x²-5x+6=7*8

x²-5x+6=56

x²-5x-50=0     D=225     √D=15

x₁=-5 ∉       x₂=10.

ответ: х=10.

Объяснение:

1.

C⁵ₓ₊₁=(3/8)*A³ₓ

(x+1)!/((x+1-5)!*5!)=(3/8)*x!/(x-3)!

(x+1)!/((x-4)!*5!)=(3/8)*x!/((x-4)!(x-3))

x!*(x+1)/5!=(3/8)*x!/(x-3)

(x+1)/5!=(3/8)/(x-3)

(x-3)*(x+1)=(3/8)*120

x²-2x-3=45

x₂-2x-48=0     D=196    √D=14

x₁=-6 ∉      x₂=8.

ответ: х=8.

2.

Cˣ⁻⁴ₓ₊₁=(7/15)*A³ₓ₊₁

(x+1)!/((x+1-(x-4))!*(x-4)!=(7/15)*(x+1)!/(x+1-3)!

(x+1)!/(5!*(x-4)!=(7/15)*(x+1)!/(x-2)!

1/(5!*(x-4)!)=(7/15)/((x-4)!*(x-3)*(x-2))

1/5!=(7/15)/((x-3)*(x-2))

15*(x-3)*(x-2)=7*5!

15*(x²-5x+6)=7*120  |÷15

x²-5x+6=7*8

x²-5x+6=56

x²-5x-50=0     D=225     √D=15

x₁=-5 ∉       x₂=10.

ответ: х=10.