（3x-y)^2-3x+y=（3x-y)(3x-y-1)
(2a+s)^2-6(2a+s)+9=(2a+s-3)^2
4(x-y)^2+4(x-y)+1=(2x-2y+1)^2
(4x^2+1)^2-16x^2=(4x^2+1+4x)(4x^2+1-4x)=（2x+1)^2(2x-1)^2
(x-y)^3+2×(y-x)^2=(x-y)^2(x-y+2)
4(3a+2x)^2-9(a-x)^2=(6a+4x+3a-3x)(6a+4x-3a+3x)=(9a+x)(3a+7x)
y-x+3(x-y)^2 =(y-x)(1+2y-2x)