Perpendiculars from four corners to diagonals

[Бк] , [Бй] , [^] , [Би]Perpendiculars from four corners to diagonals / In the case of rectangle(GC World : Various Problems ,QuadrangleБиQuadrangle)

What feature do you see when ABCD is a rectangle?

GC/Win

Forum of Geometric Constructor by Y.Iijima