4个初2的整式，看不懂说，别不留言..（过程）

①81x^4-1
=(9x^2+1)(9x^2-1)
=(9x^2+1)(3x+1)(3x-1);

②6a(b-c)^2-8a^2(c-b)^3
=6a(b-c)^2+8a^2(b-c)^3
=2a(b-c)^2[3+4a(b-c)]
=2a(b-c)^2(4ab-4ac+3);

③-2ma^2-6ma+8m
=-2m(a^2+3a-4)
=-2m(a+4)(a-1);

④应该是"x^3-x^2y-xy^2+y^3"吧!

x^3-x^2y-xy^2+y^3
=(x^3-x^2y)-(xy^2-y^3)
=x^2(x-y)-y^2(x-y)
=(x-y)(x^2-y^2)
=(x-y)(x+y)(x-y)
=(x+y)(x-y)^2.

是N次方吗