x^4-x^3-x^2+2x-2
=(x^4-x^3)-(x^2-2x+2)
=x^3(x-1)-(x-1)^2
=(x^3-x-1)*(x-1)
X4-X3-X2+2X -2= (X4-X3-X2)+(2X-2) = X2(X2-1-X)+2(X-1) = X2((X-1)(X+1)-X) +2(X-1) = X3+X2-X3(X-1)+2(X-1) = X2(X-1)-X3(X-1)+2(X-1)
=(X2-X3+2)(X-1)
Ta có : x4 - x3 - x2 + 2x - 2
= ( x4 - x3 ) - ( x2 - 2x + 2 )
= x3 . ( x - 1 ) - ( x - 1 )2
= ( x3 - x - 1 ) . ( x - 1 )