x²+y²-2x-2y-2=0
(x-1)^2+(y-1)^2=4
圆心(1,1),r=2
圆心到直线距离d=|2k|/√(10k2+12k+4)
d^2=4k2/(10k2+12k+4)
d^2(10k2+12k+4)=4k2
(10d^2-4)k2+12d^2k+4d^2=0
∆=-d^4+4d^2≥0
d^2≤4=r^2
d≤r
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