x + y = 4
y = 4 - x
x^3 + (4 - x)^3 = 28
4 (3x^2 - 12x + 16) = 28
3x^2 - 12x + 16 = 7
3x^2 - 12x + 9 = 0
x^2 - 4x + 3 = 0
x(1) = 1
x(2) = 3
y(1) = 3
y(2) = 1
ответ: (3, 1), (1, 3).
