(3x^3-2x^2+5x-2)-(4x^3-x^2+5)
=3x^3-2x^2+5x-2-4x^3+x^2-5
=-x^3-x^2+5x-7
所以
(3x^3-2x^2+5x-2)-(-x^3-x^2+5x-7)=4x^3-x^2+5