L:x-2y+4=0,k(L)=0.5
x=2y-4
B(2b-4,b),A(2,8),C(-4,2)
k(AB)=(b-8)/(2b-6),k(CB)=(b-2)/(2b)
[k(L)-k(AB)]/[1+k(L)*k(AB)]=[k(CB)-k(L)]/[1+k(L)*k(CB)]
[0.5-(b-8)/(2b-6)]/[1+0.5*(b-8)/(2b-6)]=[(b-2)/(2b)-0.5]/[1+0.5*(b-2)/(2b)]
b=10/7
B(-8/7,10/7)
L:x-2y+4=0,k(L)=0.5
x=2y-4
B(2b-4,b),A(2,8),C(-4,2)
k(AB)=(b-8)/(2b-6),k(CB)=(b-2)/(2b)
[k(L)-k(AB)]/[1+k(L)*k(AB)]=[k(CB)-k(L)]/[1+k(L)*k(CB)]
[0.5-(b-8)/(2b-6)]/[1+0.5*(b-8)/(2b-6)]=[(b-2)/(2b)-0.5]/[1+0.5*(b-2)/(2b)]
b=10/7
B(-8/7,10/7)