y=kx-1
x^2-y^2=1
x^2-(kx-1)^2=1
(1-k^2)x^2+2kx-2=0
x1+x2=2k/(k^2-1)
x1x2=2/(k^2-1)
1/2AB*h
kx-y-1=0
1/(k^2+1)^1/2
(x1-x2)^2+(y1-y2)^2=(1+k^2)(x1-x2)^2=(1+k^2)((x1+x2)^2-4x1x2)=(1+k^2)(4k^2/(k^2-1)^2-8(k^2-1)
1/2ABh=2^1/2
1/4AB^2h^2=2
AB^2h^2=8
1/(k^2+1)*(1+k^2)(4k^2/(k^2-1)^2-8(k^2-1))=8
4k^2/(k^2-1)^2-8(k^2-1)=8
k^2/(k^2-1)^2-2(k^2-1)=2
k^2-2(k^2-1)^3=2