Use the arc command to represent the upper and lower arcs, and then form a list l 1 with the line segment BD. )

Then use the tracking point h and the trajectory command.

E= tracking point (l 1).

Trajectory (E+0, e).

You can draw the track and color it. But the trajectory coloring is just a "sign" and the area cannot be calculated.

Software introduction:?

GeoGebra is a dynamic mathematics software which combines geometry, algebra and calculus. It was designed by Marcus Hornwater, a professor of mathematics at Atlanta University in Florida.

On the one hand, GeoGebra is a dynamic geometry software. You can draw points, vectors, line segments, lines, polygons, conic curves and even functions on them, and you can change their properties later.

On the other hand, you can also directly input equations and point coordinates. Therefore, GeoGebra also has the ability to handle variables (these variables can be a number, angle, vector or point coordinates), and it can also differentiate and integrate functions, find out the roots of equations or calculate the minimax of functions.

So GeoGebra has the function of dealing with algebra and geometry at the same time, so the left side of GeoGebra window is the algebra area, and the right side is the geometry area (also called drawing area), just like figure 1.