(x+3)²-(x+3)=(x+3)(x+2)a²-b²-2b-1=a²-(b-1)²=(a+b-1)(a-b+1)(x+2)(x+4)+x²-4=(x+2)(x+4)+(x+2)(x-2)=(x+2)(x+4+x-2)=2(x+2)(x+1)题目应该是:-x^4y²+4x³y³-4x²y^4-x^4y²+4x³y³-4x²y^4=-x²y²(x²+4xy-4y²)=-x²y²(x-2y)²