第1个. 6xy-3x²-3y² =-3(x²-2xy+y²)=-3(x-y)² 第二个, 4x²(x-y)+y²(y-x)=4x²(x-y)-y²(x-y)=(x-y)(4x²-y²)=(x-y)(2x+y)(2x-y)