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解:原式=1-(x-y/x-2y)÷((x+y)(x-y)/(x-2y)²)
=1-(x-y/x-2y)×((x-2y)²/(x+y)(x-y))
=1-(x-2y)/(x+y)
=(x+y)/(x+y)-(x-2y)/(x+y)
=((x+y)-(x-2y))/(x+y)
=(x+y-x+2y)/(x+y)
=3y/(x+y)
当x=2,y=5时,
原式=(3×5)/(2+5)
=15/7
化简过程中“/”都表示分数线
=1-(x-y/x-2y)×((x-2y)²/(x+y)(x-y))
=1-(x-2y)/(x+y)
=(x+y)/(x+y)-(x-2y)/(x+y)
=((x+y)-(x-2y))/(x+y)
=(x+y-x+2y)/(x+y)
=3y/(x+y)
当x=2,y=5时,
原式=(3×5)/(2+5)
=15/7
化简过程中“/”都表示分数线
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