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问题: 若7x-2y=0,则[(x/y)-(y/x)]/[(x/y)-1 (y/x)]=?

若7x-2y=0,则[(x/y)-(y/x)]/[(x/y)-1+(y/x)]=?

解答:

7x-2y=0,
即x/y=2/7
y/x=7/2

[(x/y)-(y/x)]/[(x/y)-1+(y/x)]
=[(2/7)-(7/2)]/[(2/7)-1+(7/2)]
=[(4-49)/14]/[(4+49-14)/14]
=-15/13