x^2(x-1)^2-4x(x-1)-12
= [x(x-1)] ^2 -4x(x-1)- 12
= [x(x-1) - 6 ] [x(x-1) +2 ]
= (x²-x -6 )(x² -x +2 )
= ( x -3 ) (x+2 ) (x² -x +2 )