y=kx-1
x^2-(k-1)^2=1
(1-k^2)x^2+2kx-1-k^2=0
xQ=(xA+xB)/2=-k/(1-k^2)
yQ=-1/(1-K^2)
PQ:y=(x+2)/(2k^2+k-2)
b=2/(2k^2+k-2)
2bk^2+bk-2b-2=0
b^2-4*2b*(-2b-2)≥0
b≥0,或者b≤-16/17
y=kx-1
x^2-(k-1)^2=1
(1-k^2)x^2+2kx-1-k^2=0
xQ=(xA+xB)/2=-k/(1-k^2)
yQ=-1/(1-K^2)
PQ:y=(x+2)/(2k^2+k-2)
b=2/(2k^2+k-2)
2bk^2+bk-2b-2=0
b^2-4*2b*(-2b-2)≥0
b≥0,或者b≤-16/17