[code]LocusEquation[a⊥b,C][/code] asks GeoGebra where to put point [i]C[/i] to ensure that the triangle is right at [i]C[/i]. Thales' theorem states that if (and only if) [i]C[/i] is a point of the circumcircle of the diameter [i]AB[/i], then the triangle is right.