Consider a rigid body rotating in a plane. We wish to determine the angular velocity of the rigid body given the known velocities of points A and B on the rigid body. These velocities are parallel and pointing in the same direction. The line joining points A and B is perpendicular to the direction of the velocities. The figure below illustrates the set up of the problem.
Note that lC is the intersection of the line passing through points A and B, and the line joining the tip of the vectors `v_(A) and v_(B)`