a) (x - 4)2 - (x + 3)(x - 4)= (x - 4)(x - 4 - (x + 3))
= (x - 4)(x - 4 - x - 3)
= - 7(x - 4)
b) 16 - a2 - 2ab - b2
= 16 - (a2 + 2ab + b2)
= 42 - (a + b)2
= (4 - (a + b))(4 + (a + b))
= (4 - a - b)(4 + a + b)
c) 4x2 - 17x + 13
= 4x2 - 4x - 13x + 13
= 4x(x - 1) - 13(x - 1)
= (x - 1)(4x - 13)
pn coi kt lại nhé