1)（a-b)^2-(a+b)^2
=a^2+b^2-2ab-a^2-b^2-2ab=-4ab
2)-n^2+(m+n)^2=m^2+2mn
3)4x^2-(x+y)^2
=4x^2-x^2-y^2-2xy=3x^2-y^2-2xy
4)-(b-c)^2+4a^2=-b^2-c^2+2bc+4a^2
5)(3m+2n)^2-(m-n)^2=8m^2+3n^2+14mn
6)3X^2-27=3(x+3)(x-3)
7)m^2(x-y)+n^2(y-x) =(x-y)(m+n)(m-n)