已知1/x-1/y=3,求x-2xy-y/5x+3xy-5y的值

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

已知1/x-1/y=3,求x-2xy-y/5x+3xy-5y的值
1/x-1/y=3
(Y-X)/XY=3
Y-X=3XY
X-Y=-3XY
(x-2xy-y)/(5x+3xy-5y)
=(-3XY-2XY)/(-15XY+3XY)
=-5XY/-12XY
=5/12

1/12
左边式子同乘XY 整体代入

由等式1/x-1/y=3可得x=y/（3y+1）
即原式=y/3y+1-2*[y^2/(3y+1)]-(3y+1)/5+3y^2/（3y+1)-5y
=5/12
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