xy²+2xy-3x-y²+2y-1=(xy²+2xy-3x)-(y²-2y+1)=x(y²+2y-3)-(y²-2y+1)=x(y+3)(y-1)-(y-1)²=(y-1)[x(y+3)-(y-1)]=(y-1)(xy+3x-y+1)