The figure shows a right triangle ACB,
the product of the hypotenuse and the length of the altitude
drawn to the hypotenuse equals the product of the two legs or catheti.
Geometry software that can be used to learn and research:
Geometry Expressions, Cabri, Cinderella, GeoGebra, Geometer Sketchpad, C.a.R., TracenPoche, Mathematica.