Найдите сумму корней уравнения x^3 + x^3-16x-16=0

X³ + x³ - 16x - 16 = 0
2(x + 2)(x² - 2x - 4) = 0
x + 2 = 0 и x² - 2x - 4 = 0
x = -2 и  x² - 2x = 4
x = -2 и x² - 2x + 1 = 5
x = -2 и (x + 1)² = 5
x = -2 и x - 1 = √5 и x - 1 = -√5
x = -2; 1 + √5; 1 - √5