1) -x=-16 2) -(-x)=9,4

x^4 - 16x^2 + 24x - 9 = 0
x^4 - x^3 + x^3 - x^2 - 15x^2 + 15x + 9x - 9 = 0
x^3 * (x-1) + x^2 * (x-1) - 15x * (x-1) + 9 * (x-1) = 0
(x-1) * (x^3 + x^2 - 15x + 9) = 0
x1 = 1
x^3 + x^2 - 15x + 9 = 0
x^3 - 3x^2 + 4x^2 - 12x - 3x + 9 = 0
x^2 * (x-3) + 4x * (x-3) - 3 * (x-3) = 0
(x-3) * (x^2 + 4x - 3) = 0
x2 = 3
x^2 + 4x - 3 = 0
x3,4 = -2 +- корень (7)

Х = 16
Х = 9,4
Немного странный вопрос,,,,,,,