a ) x^4 - x^3 - x^2 +1
=từ từ
b ) - x - y^2 + x^2 - y
=(x+y)(x-y) - (x+y)
= (x+y) (x-y+1)
c ) x^2 - y^2 - x - y
= Giống câu b
d ) x^2 - y^2 + 4 - 4x
= (x^2 - 2x + 4) - y^2
= (x-2)^2 - y^2
= (x+y-2) (x-y-2)
a ) x^4 - x^3 - x^2 +1
= (1+x) (1-x) - x^3(1-x)
= (-x^3 +x+1) (1-x)