当x=2007,y=2008时,求x^4-y^4/x^2-2xy-y^2÷x^2+y^2/y-x=分式的计算

当x=2007,y=2008时,求x^4-y^4/x^2-2xy-y^2÷x^2+y^2/y-x=分式的计算
当x=2007,y=2008时,求x^4-y^4/x^2-2xy-y^2÷x^2+y^2/y-x=
分式的计算

当x=2007,y=2008时,求x^4-y^4/x^2-2xy-y^2÷x^2+y^2/y-x=分式的计算
(x^4-y^4)/(x^2-2xy+y^2)÷(x^2+y^2)/(y-x)
= (x^2-y^2)(x^2+y^2)/(x^2-2xy+y^2)*(y-x)/(x^2+y^2)
= (x^2-y^2)/(x^2-2xy+y^2)*(y-x)
= (x-y)(x+y)/(x-y)^2*(y-x)
= (x+y)/(x-y)*(y-x)
= -(x+y)/(x-y)*(x-y)
= -(x+y)
=-x-y

应该是(x^4-y^4)/(x^2-2xy+y^2)÷(x^2+y^2)/(y-x)哦？
[（x^2+y^2)(x+y)(x-y)]/(x-y)^2]*[(y-x)/(x^2+y^2)]
=-x-y