quadrangle by its diagonals with sliders

This applet contains a dynamic sketch of a quadrangle GEFH constructed by its diagonals. This means that two segments E’F’, G’H’ are given, and the diagonals of the constructed quadrangle must be equal to these segments.       The segments E’F’, G’H’ are controlled by sliders f, g;        The diagonals of the quadrangle GEHF equal the given segments: E’F’=EF, G’H’=GH; the segments plotted as equal, are of the same color; they remain equal under changes caused by dragging the sliders. In addition to dragging the sliders, you may drag the vertices of the quadrangle and change it in this way, as well, still preserving the length of the given segments. Please perform all these possibilities of dragging to experience and appraise the various transformations the quadrangle GEHF undergoes as a result of each of them. The Algebra view presents the values f, g associated with the given segments, with notations in colors corresponding to the segments and to the sliders controlling them, and a value q1 associated with the quadrangle.