3x^3-4x+1=(3x^3-3)-(4x-4)=3(x-1)(x^2+x+1)-4(x-1)=(x-1)(3x^2+3x-1)
-9x2+18xy-9y2+6x-6y-1=(-9x2+18xy-9y2)+(6x-6y)-1=-9(x-y)^2+6(x-y)-1
=-[3(x-y)-1]^2=-(3x-3y-1)^2
x4+x2-2=(x^2+2)(x^2-1)=(x^2+2)(x-1)(x+1）