(8xy- x2+y2)-(x2-y2+8xy)
=8xy- x2+y2-x2+y2-8xy
=-2x2+2y2把全部的过程写出来行吗？我算的2y2...这就是过程把合并同类项的过程写出来(8xy-8xy)-(x2+x2)+(y2+y2)怎么确定这两个同类项之间的符号..你吃不准，那就带着符号-x2-x2=+(-x2-x2)=+(-2x2)=-2x2