赞 chenmengyt 幼苗
共回答了22个问题采纳率：90.9% 举报
x/y=2
x/(x-y )- y/(x+y) - y^2/(x^2-y^2)
=[x(x+y)-y(x-y)-y²]/[(x+y)(x-y)]
=(x²+xy-xy+y²-y²)/(x²-y²)
=x²/(x²-y²)
=(x/y)²/[(x/y)²-1]
=2²/[2²-1]
=4/3
x/(x-y )- y/(x+y) - y^2/(x^2-y^2)
=[x(x+y)-y(x-y)-y²]/[(x+y)(x-y)]
=(x²+xy-xy+y²-y²)/(x²-y²)
=x²/(x²-y²)
=(x/y)²/[(x/y)²-1]
=2²/[2²-1]
=4/3
1年前 追问
5
∵x/y=2
∴y/x=1/2
∴x/(x-y )- y/(x+y) - y^2/(x^2-y^2)
=1/(1-y/x)-1/(x/y+1)-1/[(x/y)²-1]
=1/(1-1/2)-1/(2+1)-1/(2²-1)
=1/(1/2)-1/3-1/3
=2-2/3
=4/3
∴y/x=1/2
∴x/(x-y )- y/(x+y) - y^2/(x^2-y^2)
=1/(1-y/x)-1/(x/y+1)-1/[(x/y)²-1]
=1/(1-1/2)-1/(2+1)-1/(2²-1)
=1/(1/2)-1/3-1/3
=2-2/3
=4/3
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