已知y/x=1/3,求式子(x^2-y^2)/(x^2+y^2-xy)的值

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已知y/x=1/3,求式子(x^2-y^2)/(x^2+y^2-xy)的值
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已知y/x=1/3,求式子(x^2-y^2)/(x^2+y^2-xy)的值
已知y/x=1/3,求式子(x^2-y^2)/(x^2+y^2-xy)的值

已知y/x=1/3,求式子(x^2-y^2)/(x^2+y^2-xy)的值
∵y/x=1/3 ∴x≠0.给原式的分子分母同时除以x²得:原式=[1-(y/x)²]/[1+(y/x)²-(y/x)]=[1-(1/3)²]/[1+(1/3)²-(1/3)]=(8/9)/[(10/9)-(1/3)]=(8/9)/[(10/9)-(3/9)]=(8/9)/(7/9)=8/7.

y/x=1/3
设y=k
x=3k

(x^2-y^2)/(x^2+y^2-xy)
=[(3k)^2-k^2)/[(3k)^2+k^2-3k*k]
=8k^2/7k^2
=8/7