a/ x3 + 27 - 3x.(x+3)
= x3 + 33 - 3x.(x+3)
= (x+3).(x2 - 3x + 9) - 3x.(x+3)
= (x+3).(x2 - 3x + 9 - 3x)
= (x+3).(x2 - 6x + 9)
= (x+3).(x2 - 2.x.3 + 32)
= (x+3).(x-3)2
b/ x3 + 2x2y + xy2 - 9x
= x.(x2 + 2xy + y2 - 9)
= x.[(x+y)2 - 32]
= x.(x+y+3).(x+y-3)