y^3+27=y^3+3^3=(y+3)(y^2-3y+9)
x^2+6x+9=(x+3)^2
x^3+2x^2+x+2=x(x^2+1)+2(x^2+1)
4x-4y+xy-y^2=4(x-y)+y(x-y)
y^3+27=y^3+3^3=(y+3)(y^2-3y+9)
x^2+6x+9=(x+3)^2
x^3+2x^2+x+2=x(x^2+1)+2(x^2+1)
4x-4y+xy-y^2=4(x-y)+y(x-y)