Let AB be a diameter of a circle S, and let L be the tangent at A. Furthermore, let c be a fixed, positive real, and consider all pairs of points X and Y lying on L, on opposite sides of A, such that |AX|\cdot |AY| \equal{} c. The lines BX and BY intersect S at points P and Q, respectively. Show that all the lines PQ pass through a common point. trigonometrygeometrycircumcircleradical axisgeometry unsolved