已知x/y=3/5求(x^2-xy)/(x^2-2xy+y^2)-(x+y)/(x-y）的值
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x/y=3/5
设
x=3k
y=5k
则
(x^2-xy)/(x^2-2xy+y^2)-(x+y)/(x-y）
=x(x-y)/(x-y)(x-y)-(x+y)/(x-y）
=x/(x-y) - (x+y)/(x-y)
=y/(y-x)
=5k/(5k-3k)
=5k/2k
=5/2
=2.5
设
x=3k
y=5k
则
(x^2-xy)/(x^2-2xy+y^2)-(x+y)/(x-y）
=x(x-y)/(x-y)(x-y)-(x+y)/(x-y）
=x/(x-y) - (x+y)/(x-y)
=y/(y-x)
=5k/(5k-3k)
=5k/2k
=5/2
=2.5
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x/y=3/5 可设：x=3k，y=5k
(x^2-xy)/(x^2-2xy+y^2)-(x+y)/(x-y）
=x(x-y)/(x-y)^2-(x+y)/(x-y)
=x/(x-y)-(x-y)/(x-y)
=[x-(x-y)]/(x-y)
=y/(x-y)
=5k/(3k-5k)
=-5/2
(x^2-xy)/(x^2-2xy+y^2)-(x+y)/(x-y）
=x(x-y)/(x-y)^2-(x+y)/(x-y)
=x/(x-y)-(x-y)/(x-y)
=[x-(x-y)]/(x-y)
=y/(x-y)
=5k/(3k-5k)
=-5/2
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5/2
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