1.=(x-y)[(a-b)-(b-a)]
=(x-y)(2a-2b)
=2（x-y）(a-b)
2,=4+12x-12y+9x+9y
=21x-3y+4
3,=x(x^2-3^2)
=x(x+3)(x-3)
4,=(4x)^2-1
=(4x^2+1)(4x^2-1)
= (4x^2+1)(2x+1)(2x-1)
5,6xy^2-9x^2y-y^3
=y(6xy-9x^2-y^2)
=-y（x-y）^2
6,=4a^2+b^2-4ab+8ab
=(2a)^2+b^2+4ab
=(2a+b)^2
^2 表示平方