4mn^2-4m^2n-n^3
=n(4mn-4m^2-n^2)
=-n(n-2m)^2
16m^2-4(m+n)^2
=4(2m+m+n)(2m-m-n)
=4(3m+n)(m-n)
(x^2-6)^2-6(x^2-6)+9
=(x^2-6-3)^2
=(x^2-9)^2
=(x+3)^2(m-3)^2
x^2(x-y)+y^2(y-x)
=x^2(x-y)-y^2(x-y)
=(x-y)(x^2-y^2)
=(x-y)^2(x+y)
(x+y)^2-4xy
=x^2+2xy+y^2-4xy
=x^2-2xy+y^2
=(x-y)^2