German chordal quadrilateral
Source: German TST 3, P1, 2009, Exam set by Gunther Vogel
July 18, 2009
geometry unsolvedgeometry
Problem Statement
Let be a chordal/cyclic quadrilateral. Consider points on and on with
\overline{AP}: \overline{PB} \equal{} \overline{CS}: \overline{SD}, \overline{AQ}: \overline{QB} \equal{} \overline{CR}: \overline{RD}.
How to choose such that \overline{PR} \cdot \overline{AB} \plus{} \overline{QS} \cdot \overline{CD} is minimal?