(X-y)(x-2y)+(X-2Y)(X-3Y)-2(X-3Y)(X-4Y)=(x-2y)(x-y+x-3y)-2(x-3y)(x+4y)=(x-2y)(2x-4y)-2(x-3y)(x+4y)=2x²-4xy-4xy+8y²-2x²-16xy+6xy+24y²=-18xy+32y²=-18x4x3/2+32x(3/2)²=-108+20...书上答案是0，你说的不对(X-y)(x-2y)+(X-2Y)(X-3Y)-2(X-3Y)(X-4Y) =(x-2y)(x-y+x-3y)-2(x-3y)(x-4y) =(x-2y)(2x-4y)-2(x-3y)(x-4y) =2x²-4xy-4xy+8y²-2(x²-4xy-3xy+12y²) =2x²-4xy-4xy+8y²-2x²+8xy+6xy-24y² =6xy-16y² =6x4x3/2-16x(3/2)² =36-36 =0祝学习进步，望采纳~~