x+y=-3
xy+x+y = -2
两式相减得xy = 1
x/y + y/x
= (x^2+y^2) / xy
= ( (x+y)^2-2xy) / xy
= (9-2)/1
= 7
x+y=-3 xy+x+y=-2 x/y+y/x=?
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