[list=1][*]Given the triangle ABC.[br][/*][*]Construct the lines of the sides.[/*][*]Let D be an arbitrary point.[/*][/list]In Steps 4-9 we create the perpendicular projection of D to the lines constructed in Step 2.[br]Is it possible to choose D in order to be the projection points (feet points E, F and G) aligned?[br]In Step 10 GeoGebra solves this question by computing [code]LocusEquation[AreCollinear[E,F,G],D][/code].