f(x)= 4x + 8 - 6 * (x + 2)^(2/3)
f(x) = 0
4x + 8 - 6 * (x + 2)^(2/3) = 0
4 * (x + 2) - 6 * (x + 2)^(2/3) = 0
2 * (x + 2)^(2/3) * (2 * (x + 2)^(1/3) - 3) = 0
Получаем либо x = - 2, либо
2 * (x + 2)^(1/3) - 3 = 0
(x + 2)^(1/3) = 3/2
x + 2 = 27/8
x = 11/8
Осталось записать промежутки и определить знаки.