已知1/x-1/y=5,求(2y+3xy-2x)/(-4x+2xy+4y)的值

(2y+3xy-2x)/(-4x+2xy+4y)
=(2/x+3-2/x)/(-4/y+2+4/x) 分子分母同时除以xy
=[-2(1/x-1/y)+3]/[4(1/x-1/y)+2]
=(-10+3)/(20+2)
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