初一数学代数式求值，已知1/x-1/y=3，求(2x-14xy-2y)/(x-2xy-y)
\u5df2\u77e51/X-1/Y=3\uff0c\u5219\u4ee3\u6570\u5f0f\uff082X-14XY-2Y\uff09/\uff08X-2XY-Y\uff09\u7684\u503c\u89e3\uff1a
\u75311/x-1/y=1,\u53d8\u5f62
\u4e24\u8fb9\u5404\u4e58\u4ee5xy\uff0c\u5f97\uff0cy-x=3xy,\u2234xy=1/3(y-x),
\uff082x-14xy-2y\uff09/\uff08x-2xy-y\uff09
=[2x-14/3(y-x)-2y]/ [ x-2/3(y-x)-y) ],
\u5206\u5f0f\u4e0a\u4e0b\u5404\u4e58\u4ee53\uff0c\u5e76\u5c55\u5f00\u62ec\u53f7\uff0c\u5f97
3(2x-14/3y+14/3x-2y)/3(x-2/3y+2/3x-y)
=(6x-14y+14x-6y)/(3x-2y+2x-3y)
=(20x-20y)/(5x-5y)
=4(5x-5y)/(5x-5y)
=4
1/x-1/y=3
y-x=3xy
\u6240\u4ee5\uff1a2x-14xy-2y=2(x-y)-14xy=2(-3xy)-14xy=-20xy
x-2xy-y=-3xy-2xy=-5xy
\u6240\u4ee5\uff1a
(2x-14xy-2y)/(x-2xy-y)=-20xy/(-5xy)=4
通分
(y-x)/xy=3
y-x=3xy
x-y=-3xy
原式=[2(x-y)-14xy]/[(x-y)-2xy]
=[2(-3xy)-14xy]/[(-3xy)-2xy]
=-20xy/(-5xy)
=4
(2x-14xy-2y)/(x-2xy-y)
=（2/y-14-2/x）/(1/y-2-1/x) 即分母分子同时除以xy
=(-6-14)/(-3-2) 即将1/x-1/y=3代入
=4
(2x-14xy-2y)/(x-2xy-y)
=（2/y-2/x-14）/(1/y-1/x-2)
=(-3*2-14)/(-3-2)
=(-20)/(-5)
=4
x-y=-3xy
(2x-14xy-2y)/(x-2xy-y)=4
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