-12x的3次方+12x的2次方y-3xy的2次方=-3x(4x²-4xy+y²)=-3x(2x-y)².-20a+5a的2次方-15ab=5a²-15ab-20a=5a(a-3b-4).-x的2次方-4y的2次方+4xy=-(x²-4xy+4y²)=-(x-2y)²...