Problem 609: Triangle, Perpendiculars, 90 Degrees, Collinearity.
Level: Mathematics Education, High School, College
The figure shows a triangle ABC with a point
DE is perpendicular to DC (E is on BA extended), DF is perpendicular to
DA (F is on BC extended), and DG is perpendicular to DB (G is on AC
extended). Prove that points E, F, G are collinear.