
已知:y=2x-5,求代数式[(x^2+y^2)-(x+y)^2-2y(x-y)]÷8y的值
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y=2x-5 y-2x=-5
[(x^2+y^2)-(x+y)^2-2y(x-y)]÷8y=[x^2+y^2-x^2-y^2-2xy-2y(x-y)]÷8y=[-2xy-2y(x-y)]÷8y
=y[-2x-2x+2y]÷8y=-(y-2x)/4 =5/4
[(x^2+y^2)-(x+y)^2-2y(x-y)]÷8y=[x^2+y^2-x^2-y^2-2xy-2y(x-y)]÷8y=[-2xy-2y(x-y)]÷8y
=y[-2x-2x+2y]÷8y=-(y-2x)/4 =5/4
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