已知x+y=-2,xy=-1,求（y+1/x+1）+（x+1/y+1)
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（y+1/x+1）+（x+1/y+1)
=(y+1)²/[(x+1)(y+1)]+(x+1)²/[(x+1)(y+1)]
=[(y+1)²+(x+1)²]/[(x+1)(y+1)]
=(y²+2y+1+x²+2x+1)/(xy+x+y+1)
=[(x+y)²-2xy+2(x+y)+2]/(xy+x+y+1)
=(4+2-4+2)/(-1-2+1)
=4/(-2)
=-2
=(y+1)²/[(x+1)(y+1)]+(x+1)²/[(x+1)(y+1)]
=[(y+1)²+(x+1)²]/[(x+1)(y+1)]
=(y²+2y+1+x²+2x+1)/(xy+x+y+1)
=[(x+y)²-2xy+2(x+y)+2]/(xy+x+y+1)
=(4+2-4+2)/(-1-2+1)
=4/(-2)
=-2
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