Solution to the above question:

As the red circles move about segment , they cover the area we are looking for. On the left side, the circle must move around pivoted on . On the right side, the circle must move pivoted on However, at the top and bottom, the circle must lie on both A and B, giving us our upper and lower bounds.

This egg-like shape is .

The area of the region can be found by dividing it into several sectors, namely