1) (d-b)/(a-b)=(x2-x1)/(y2-y1).

2) (a-x1)^2 + (b-y1)^2 = t^2
3) (a-x2)^2 + (b-y2)^2 = t^2
4) (x2-x1)^2 + (y2-y1)^2 = t^2

x1 = a-t*(d-b+sqrt(k^2-3*(d-b)^2))/(2*k)
y1 = b+t*((d-b)*sqrt(k^2-3*(d-b)^2)-(a-c)^2)/(2*k*(a-c))
x2 = a-t*(d-b-sqrt(k^2-(d-b)^2))/(2*k)
y2 = b+t*(2*(d-b)*(a-c)-(a-c)^2+(d-b)*sqrt(k^2-3*(d-b)^2))/(2*k*(a-c))