(x-y+1)/(x+y+1)
=[(x+y+1)-(2y)]/(x+y+1)
=1-(2y)/(x+y+1)
=1-2/[(x+1)/y+1)]
(x+1)/y可以看成点(x,y)和点(-1,0)连线斜率的倒数
点(x,y)还是圆
你这题有点问题