已知y-2x=0,求代数式（x^+xy+y^）（x^—y^)/(x^-y^)(x^-xy+y^) 对....

已知y-2x=0,求代数式（x^+xy+y^）（x^—y^)/(x^-y^)(x^-xy+y^) 对....
已知y-2x=0,求代数式（x^+xy+y^）（x^—y^)/(x^-y^)(x^-xy+y^)
对....

已知y-2x=0,求代数式（x^+xy+y^）（x^—y^)/(x^-y^)(x^-xy+y^) 对....
题目应是 已知y-2x=0,求代数式(x^2+y^2)(x^2-xy+y^2)\(x^2+xy+y^2)(x^2-y^2)
y-2x=0
y=2x
(x^2-y^2)(x^2-xy+y^2)/(x^2+xy+y^2)(x^2-y^2).
=(x^2-xy+y^2)/(x^2+xy+y^2)
=(x^2-2x^2+4x^2)/(x^2+2x^2+4x^2)
=3x^2/7x^2
=3/7

那么首先上下同时削掉一个（x^—y^)
然后因为y-2x=0，所以y=2x
带入即可