B. 4088. P is an interior point of side B1B2 of an acute-angled triangle AB1B2. Let Q denote the reflection of P about point A. Let Di denote the perpendicular projection of P onto the line segment ABi, and let Fi be the midpoint of the line segment DiBi. Prove that if QD1 is perpendicular to PF1, then QD2 is perpendicular to PF2.
Suggested by J. Bodnár, Budapest
Solution (in Hungarian)