Salinon (from the name of an antique greek shield): The area indicated by the yellow color is equal to the area of the circle with diameter BC. (Switch to Ctrl+2 and move A, look at the compound area, computed with the help of the formula).

In the formula, x is the area of circle-quadrant ADEB, y the area of the circle quadrant AFGC and z the area of the circle with diameter DF.

Switch to the pick-move tool (Ctrl+2) catch and move points A, B, C.