a) x2 - 9 + (x - 3)2
= (x - 3)(x + 3) + (x - 3)2
= (x - 3)(x + 3 + x - 3)
= 2x(x - 3)
b) x3 - 4x2 + 4x - xy2
= x(x2 - 4x + 4 - y2)
= x\(\left [ (x - 2)^{2} - y^{2} \right ]\)
= x(x - 2 - y)(x - 2 + y)
c) x3 - 4x2 + 12x - 27
= x3 - 27 - 4x2 + 12x
= (x - 3)(x2 + 3x + 9) - 4x(x - 3)
= (x - 3)(x2 + 3x - 4x + 9)
= (x - 3)(x2 - x + 9)