Ответ:

a) x² + 6x + 8 = x² + 2x + 4x + 8 = x (x + 2) + 4 (x + 2) = (х + 4) × (х + 2)

б) х² - 8х + 15 = х² - 5х - 3х + 15 = х (х - 5) - 3 (х - 5) = (х - 3) × (х - 5)