x⁴ - 4x³ + 16x - 16 = (x⁴ - 16) - (4x³ - 16x) = (x² - 4)(x² + 4) - 4x(x² - 4) =
= (x² - 4)(x² + 4 - 4x) = (x - 2)(x + 2)(x² - 4x + 4) = (x - 2)(x + 2)(x-2)² =
= (x - 2)³(x + 2)
x⁴ - 4x³ + 16x - 16 = (x⁴ - 16) - (4x³ - 16x) = (x² - 4)(x² + 4) - 4x(x² - 4) =
= (x² - 4)(x² + 4 - 4x) = (x - 2)(x + 2)(x² - 4x + 4) = (x - 2)(x + 2)(x-2)² =
= (x - 2)³(x + 2)