9x^4+12x^3-3x^2-7x+2004=9x^4-3x^2+12x^3-7x+2004
=3x*(3x^3-x)+12x^3-7x+2004 因为3x³-x=13
=39x+12x^3-7x+2004
=12x^3-4x+36x+2004
=36x+2056
这题有问题吧,-43x吧我也觉得题目有问题，老师讲完再给回答吧