x4+y2x2+y4
=x^4+2y^2x^2+y^4-x^2y^2
=( x^2+y^2)^2--x^2y^2
=( x^2+y^2+xy)( x^2+y^2-xy)
x3+x2y-xy2-y3
=(x-y)(x^2+xy+y^2)+xy(x-y)
=(x-y)(x^2+xy+y^2+xy)
=(x-y)(x+y)^2
(x2+x)-8(x2+x)+12
= (x^2+x-6)(x^2+x-2)
=(x+3)(x-2)(x-1)(x+2)