已知x=3y,试求(x-y)^2+2xy-y^2/x^2+7xy+y^2

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已知x=3y,试求(x-y)^2+2xy-y^2/x^2+7xy+y^2
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已知x=3y,试求(x-y)^2+2xy-y^2/x^2+7xy+y^2
已知x=3y,试求(x-y)^2+2xy-y^2/x^2+7xy+y^2

已知x=3y,试求(x-y)^2+2xy-y^2/x^2+7xy+y^2
[(x-y)^2+2xy-y^2]/[x^2+7xy+y^2]
=[x²-2xy+y²+2xy-y²]/[x^2+7xy+y^2]
=x²/[x^2+7xy+y^2]
x=3y
x²/[x^2+7xy+y^2]
=9y²/[9y²+21y²+y²]
=9y²/31y²
=9/31

(x-y)^2+2xy-y^2/x^2+7xy+y^2
=(4y²+6y²-y²﹚/﹙9y²+21y²+y²﹚
=9/31