$\text { Đáp án: }$
` x⁴ - 5x² + 8x - 12 `
` = x⁴ - 2x³ + 2x³ - 4x² - 4x² + 2x + 6x - 12 `
` = x³(x - 2) + 2x²(x - 2) - x(x - 2) + 6(x - 2) `
` = (x³ + 2x² - x + 6)(x - 2) `
` = (x³ - x² + 3x² - 3x + 2x + 6)(x - 2) `
` = {x²(x + 3) - x(x + 3) + 2(x + 3)}(x - 2) `
` = (x² - x + 2)(x + 3)(x - 2) `