x²-y²/x²+2xy+y² 减 x+y/x-y ，其中x=1 ,y=-3 这道题怎么算？【先化简再求值，要详细
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x²-y²/x²+2xy+y² － x+y/x-y
=(x+y)(x-y)/(x+y)²-(x+y)/(x-y)
=(x-y)/(x+y)-(x+y)/(x-y)
=[(x-y)²-(x+y)²]/[(x+y)(x-y)]
=-4xy/(x²-y²)
=-4×1×(-3)/(1-9)
=3/2
=(x+y)(x-y)/(x+y)²-(x+y)/(x-y)
=(x-y)/(x+y)-(x+y)/(x-y)
=[(x-y)²-(x+y)²]/[(x+y)(x-y)]
=-4xy/(x²-y²)
=-4×1×(-3)/(1-9)
=3/2
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