(3mx的平方-2xy+3-2nx)-2(nxy+x的平方-7my)=3mx²-2xy+3-2nx-2nxy-2x²+14my=(3m-2)x²+(-2-2n)xy-2nx+14my+3∵不含有二次项∴3m-2=0-2-2n=0∴m=2/3n=1∴代数式是:-2nx+14my+3=-2x+28y/3+3当x=2,y=-3时 ...