3x（a-b）+2y（a-b）=(3x+2y)(a-b)
a^2（y-3）+（3-y）=a^2（y-3）-（y-3)=(a^2-1)(y-3)
x^2（x-y)-(x-y)=(x^2-1)(x-y)
4xy-4x^2y-y=y(4x-4x^2-1)=-y(4x^2-4x+1)=-y(2x-1)^2
(3a+2)^2-(a-6）^2=(3a+2+a-6)(3a+2-a+6)=(4a-4)(2a+8)=8(a-1)(a+4)
x^4-8x^2+16=(x^2-4)^2=(x+2)^2(x-2)^2