Answer:
2×sqrt(2) = 2.828427125...
Explanation:
x = "a positive number"
x + 56/x = x³
x² + 56 = x⁴
x⁴ - x² - 56 = 0
(x² + 7)(x² - 8) = 0
this is true only for
x² = -7
or
x² = 8
x² = -7 would mean that x is an imaginary number. so, that is not a valid solution here.
x² = 8 means
x = sqrt(8) = sqrt(4×2) = 2×sqrt(2) = 2.828427125...