8. The radius of the circle of inversion is sqrt(K^2-M^2).
This length can be constructed: draw a line, draw a point
on the line, mark a distance m on either side of the point
on the line, from each of these points draw a circle of
radius k, the radius of the inversion circle is the distance
from the circle intersections to the original point on the line.
This sketch pad drawing shows the linkage and the circle of inversion.