x乘以x^4+x^2(x^3-1)-2x^3(x+1)^2
=x^5+x^5-x^2 -2x^3(x^2+2x+1)
=x^5+x^5-x^2-2x^5-4x^4-2x^3
=-4x^4-2x^3-x^2