X = 2 + log2(y)
y^x = 256
y^x = 256
(2^log2(y))^x = 256
2^(xlog2(y)) = 2^8
x*log2(y) = 8
{x = 2 + log2(y) -> log2(y) = x - 2}
x * (x-2) = 8
x^2 - 2x - 8 = 0
(x - 4)(x + 2) = 0
1) x = 4 -> log2(y) = 4 - 2 = 2 -> y = 2^2 = 4
2) x = -2 -> log2(y) = -2 - 2 = -4 -> y = 1/16
--> два решения: x = 4, y = 4 и x = -2, y = 1/16
Произведение = 4*4*1/16*(-2) = -2