设多项式是A则(x²-2)+A=2x-4A=(2x-4)-(x²-2)所以正确是(x²-2)-A=(x²-2)-[(2x-4)-(x²-2)]=(x²-2)-(2x-4)+(x²-2)=2(x²-2)-(2x-4)=2x²-4-2x+4=2x²-2x
