（2x+1)(3x2+5x+7)=(3x-1)(2x2+5x+7)6x3+10x2+2x+3x2+5x+1=6x3+15x2+21x-2x2-5x-76x3+13x2+7x+1=6x3+13x2+16x-79x=8,x=8/9算起来有点麻烦,要细心点哦~