6x3 + 5x2 - 7x - 4
= (6x3 + 5x - 7x) - 4
= x (6x2 - 5 - 7) - 22
= x (6x2 - 12) - 22
= x [6 (x2 - 2)] - 22
= x [6 (x2 - \(\sqrt{2}^2\))] - 22
= x [6 (x +\(\sqrt{2}\)) (x -\(\sqrt{2}\))] - 22
= (x - 22) [6 (x +\(\sqrt{2}\)) (x -\(\sqrt{2}\))
b) 2x3 - x2 + x - 2
= (2x3 - x2 - x) - 2
= x (2x2 - x - 1) - 2
= (x - 2) (2x2 - x - 1)
(mik ko biet dug ko, neu sai mog bn thog cam)