Factor x2−10x+21x^2 - 10x + 21x2−10x+21.
(x−5)(x−5)(x - 5)(x - 5)(x−5)(x−5)
(x−3)(x−7)(x - 3)(x - 7)(x−3)(x−7)
(x−2)(x−9)(x - 2)(x - 9)(x−2)(x−9)
(x+3)(x+7)(x + 3)(x + 7)(x+3)(x+7)