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)

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$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)$

可以代入：y-2x=0,y=2x
原式=[x^2+(2x)^2][x^2-x*(2x)+(2x)^2]/[x^2+x*(2x)+(2x)^2][x^2-(2x)^2]
=(x^2+4x^2)(x^2-2x^2+4x^2)/(x^2+2x^2+4x^2)(x^2-4x^2)
=(5x^2*3x^2)/(7x^2*-3x^2)
=-5/7

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