Various magnitudes, of a right-angled triangle

Idan Tal
The applet demonstrates various magnitudes, which serve as signs for the existence of a right-angled triangle. At any stage it is possible to drag two vertices of the triangle and thus change the lengths of the sides and see the effect on the radii of incircles and excircles of the triangle, the area and half the perimeter of the triangle. These magnitudes are shown, on every stage, on the computer  screen, allow using formulas to determine that it is a right-angled triangle.