$\displaystyle \begin{array}{{>{\displaystyle}l}} a^{3} x-ab+b-x\\ =x\left( a^{3} -1\right) -b( a-1)\\ =x( a-1)\left( a^{2} +a+1\right) -b( a-1)\\ =( a-1)\left( a^{2} x+xa+x-b\right) \ \\ 2) x^{3} -4x^{2} +4x-1\\ =x^{3} -1-4x( x-1)\\ =( x-1)\left( x^{2} +x+1\right) -4x( x-1)\\ =( x-1)\left( x^{2} +x+1-4x\right)\\ =( x-1)\left( x^{2} -3x+1\right)\\ 3.) 3a( a-b) +b-a\ \\ =3a( a-b) -( a-b)\\ =( a-b)( 3a-1) \ \\ 4) \ không\ nhìn\ rõ\ đề\ \\ 5) 4x-x^{2} +5\\ 5x+5-x-x^{2}\\ =5( x+1) -x( x+1)\\ =( x+1)( 5-x) \ \\ 6) 3x-2x^{2} -1\\ =2x-2x^{2} +x-1\\ =2x( 1-x) -( 1-x)\\ =( 2x-1)( 1-x) \ \\ 7) ax-ay+bx-by\\ =a( x-y) +b( x-y)\\ =( a+b)( x-y) \ \\ 8) \ y^{2} -y-12=0\ \\ =y^{2} -3y+4y-12=0\ \\ =y( y-3) +4( y-3) =0\\ =( y-3)( y+4) =0\ \\ 9) \ 2x^{2} -y^{2} +xy\\ =2x^{2} +2xy-y^{2} -xy\\ =2x( x+y) -y( x+y)\\ =( 2x-y)( x+y)\\ \end{array}$
