1.4xy^2-4x^2y-y^3
原式=y(4xy-4x^2-y^2)
=-y(4x^2-4xy+y^2)
=-y(2x-y)^2
2.-a+2a^2-a^3
原式=-a(1-2a+a＾2)
=-a(1-a)＾2