Consider skew lines PP′, QQ′ and points X, Y lying on them, respectively. Initially, we have X=P, Y=Q. Both points X, Y start moving simultaneously along the rays PP′, QQ′ with the speeds c1, c2, respectively. Show that midpoint Z of segment XY always lies on a fixed ray RR′, where R is midpoint of PQ. 3D geometryfixed lineskew line