有这样一道题：计算（x-y）[(x+y)(x+y)-xy]+(x+y)[(x-y)(x-y)+xy]的值,其中x=2006,y=2008.小明同学把y=2008错抄成Y=2080,但他把计算结果算出来也是对的这是为什么?一定加分急啊.

（x-y）[(x+y)(x+y)-xy]+(x+y)[(x-y)(x-y)+xy]=(x-y)(x+y)^2-（x-y)xy+(x+y)(x-y)^2+(x+y)xy
=(x-y)(x+y)(x+y+x-y)+xy(x+y-x+y)=2x(x^2-y^2)+2xy^2=2x^3
把算式展开然后合并同类项,就可把含有y的消掉 计算出的结果就是一样的