因式分解 超急的啦~~~

不好意思，看到时太晚了

(x+y-2xy)(x+y-2)+(1-xy)^2
=（x+y)^2-2xy(x+y)-2(x+y)+4xy+1-2xy+x^2y^2
=[(x+y)^2-2(x+y)+1]-[2xy(x+y)-2xy]+x^2y^2
=(x+y-1)^2-2xy(x+y-1)+x^2y^2
=(x+y-1-xy)^2
=(xy-x-y+1)^2
=(x-1)^2(y-1)^2

-a^3-4a^2+12a
=-a(a^2+4a-12)
=-a(a-2)(a+6)

第一道不会
第二道.-a^3-4a^2+12a
=-a(a^2+4a-12)
=-a(a-2)(a+6)