3) решите уравнение x^3 + 2x^2 - 4x - 8 = 0

(x³ + 2x²) - (4x + 8) = 0
x²(x + 2) - 4(x + 2) = 0
(x + 2)(x² - 4) = 0
(x + 2)(x - 2)(x + 2) = 0
(x + 2)²(x - 2) = 0
x + 2 = 0  или  x - 2 = 0
x = - 2                x = 2