везде метод интервалов
3.
2x² - 16 < 0
x² - 8 < 0
(x - √8)(x + √8) < 0
-(-√8) (√8)
x∈ (-√8, √8)
4
x³ - 9x ≥ 0
x(x² - 9) ≥ 0
x(x - 3)(x + 3) ≥ 0
[-3] [0] [3]
x ∈ [-3, 0] U [3, +∞)
6
(x² - 25)/(x² + 9x + 8) > 0
(x - 5)(x + 5)/(x + 1)(x + 8) > 0
-(-8) (-5) (-1) (5)
x ∈ (-∞, -8) U (-5, 1) U (5, +∞)
